diff --git a/.eslintrc.js b/.eslintrc.js
index 5ecf3f5e98..1b2476bf3d 100644
--- a/.eslintrc.js
+++ b/.eslintrc.js
@@ -14,6 +14,9 @@ module.exports = {
     settings: {
         react: { version: "18" }
     },
+    ignorePatterns: [
+        '/packages/playwright/bundles/expect/third_party/**/*'
+    ],
     overrides: [
         {
             files: ['./examples/**/*'],
@@ -34,7 +37,7 @@ module.exports = {
     rules: {
         "@typescript-eslint/no-unused-vars": [2, {args: "none"}],
         "@typescript-eslint/consistent-type-imports": [2, {disallowTypeAnnotations: false}],
-        // "@typescript-eslint/no-unnecessary-condition": [2],
+        "@typescript-eslint/no-unnecessary-condition": [2],
 
         /**
          * Enforced rules
diff --git a/packages/html-reporter/src/reportView.tsx b/packages/html-reporter/src/reportView.tsx
index db95dd412c..1b37aea0ca 100644
--- a/packages/html-reporter/src/reportView.tsx
+++ b/packages/html-reporter/src/reportView.tsx
@@ -78,7 +78,7 @@ export const ReportView: React.FC<{
   return <div className='htmlreport vbox px-4 pb-4'>
     <main>
       {report?.json() && <HeaderView stats={report.json().stats} filterText={filterText} setFilterText={setFilterText}></HeaderView>}
-      {report?.json().metadata && <MetadataView {...report?.json().metadata as Metainfo} />}
+      {report?.json().metadata && <MetadataView {...report.json().metadata as Metainfo} />}
       <Route predicate={testFilesRoutePredicate}>
         <TestFilesHeader report={report?.json()} filteredStats={filteredStats} />
         <TestFilesView
diff --git a/packages/html-reporter/src/testCaseView.tsx b/packages/html-reporter/src/testCaseView.tsx
index 38eaeb3f13..6e5e629963 100644
--- a/packages/html-reporter/src/testCaseView.tsx
+++ b/packages/html-reporter/src/testCaseView.tsx
@@ -47,7 +47,7 @@ export const TestCaseView: React.FC<{
   }, [test]);
 
   const visibleAnnotations = React.useMemo(() => {
-    return test?.annotations?.filter(annotation => !annotation.type.startsWith('_')) || [];
+    return test?.annotations.filter(annotation => !annotation.type.startsWith('_')) || [];
   }, [test?.annotations]);
 
   return <div className='test-case-column vbox'>
@@ -58,10 +58,10 @@ export const TestCaseView: React.FC<{
       <div style={{ width: 10 }}></div>
       <div className={clsx(!next && 'hidden')}><Link href={testResultHref({ test: next }) + filterParam}>next »</Link></div>
     </div>}
-    {test && <div className='test-case-title'>{test?.title}</div>}
+    {test && <div className='test-case-title'>{test.title}</div>}
     {test && <div className='hbox'>
       <div className='test-case-location'>
-        <CopyToClipboardContainer value={`${test?.location.file}:${test?.location.line}`}>
+        <CopyToClipboardContainer value={`${test.location.file}:${test.location.line}`}>
           {test.location.file}:{test.location.line}
         </CopyToClipboardContainer>
       </div>
@@ -69,7 +69,7 @@ export const TestCaseView: React.FC<{
       <div className='test-case-duration'>{msToString(test.duration)}</div>
     </div>}
     {test && (!!test.projectName || labels) && <div className='test-case-project-labels-row'>
-      {test && !!test.projectName && <ProjectLink projectNames={projectNames} projectName={test.projectName}></ProjectLink>}
+      {!!test.projectName && <ProjectLink projectNames={projectNames} projectName={test.projectName}></ProjectLink>}
       {labels && <LabelsLinkView labels={labels} />}
     </div>}
     {!!visibleAnnotations.length && <AutoChip header='Annotations'>
@@ -80,7 +80,7 @@ export const TestCaseView: React.FC<{
         id: String(index),
         title: <div style={{ display: 'flex', alignItems: 'center' }}>{statusIcon(result.status)} {retryLabel(index)}</div>,
         render: () => <TestResultView test={test!} result={result} />
-      })) || []} selectedTab={String(selectedResultIndex)} setSelectedTab={id => setSelectedResultIndex(+id)} />}
+      }))} selectedTab={String(selectedResultIndex)} setSelectedTab={id => setSelectedResultIndex(+id)} />}
   </div>;
 };
 
diff --git a/packages/html-reporter/src/testFileView.tsx b/packages/html-reporter/src/testFileView.tsx
index 2113c008ff..b6689c14c7 100644
--- a/packages/html-reporter/src/testFileView.tsx
+++ b/packages/html-reporter/src/testFileView.tsx
@@ -86,9 +86,9 @@ function videoBadge(test: TestCaseSummary): JSX.Element | undefined {
   return resultWithVideo ? <Link href={testResultHref({ test, result: resultWithVideo, anchor: 'attachment-video' })}  title='View video' className='test-file-badge'>{video()}</Link> : undefined;
 }
 
-function traceBadge(test: TestCaseSummary): JSX.Element | undefined {
+function traceBadge(test: TestCaseSummary): JSX.Element {
   const firstTraces = test.results.map(result => result.attachments.filter(attachment => attachment.name === 'trace')).filter(traces => traces.length > 0)[0];
-  return firstTraces ? <Link href={generateTraceUrl(firstTraces)} title='View trace' className='test-file-badge'>{trace()}</Link> : undefined;
+  return <Link href={generateTraceUrl(firstTraces)} title='View trace' className='test-file-badge'>{trace()}</Link>;
 }
 
 const LabelsClickView: React.FC<React.PropsWithChildren<{
diff --git a/packages/html-reporter/src/testFilesView.tsx b/packages/html-reporter/src/testFilesView.tsx
index 332cff7ee3..f7091633de 100644
--- a/packages/html-reporter/src/testFilesView.tsx
+++ b/packages/html-reporter/src/testFilesView.tsx
@@ -72,8 +72,8 @@ export const TestFilesHeader: React.FC<{
       {report.projectNames.length === 1 && !!report.projectNames[0] && <div data-testid='project-name' style={{ color: 'var(--color-fg-subtle)' }}>Project: {report.projectNames[0]}</div>}
       {filteredStats && <div data-testid='filtered-tests-count' style={{ color: 'var(--color-fg-subtle)', padding: '0 10px' }}>Filtered: {filteredStats.total} {!!filteredStats.total && ('(' + msToString(filteredStats.duration) + ')')}</div>}
       <div style={{ flex: 'auto' }}></div>
-      <div data-testid='overall-time' style={{ color: 'var(--color-fg-subtle)', marginRight: '10px' }}>{report ? new Date(report.startTime).toLocaleString() : ''}</div>
-      <div data-testid='overall-duration' style={{ color: 'var(--color-fg-subtle)' }}>Total time: {msToString(report.duration ?? 0)}</div>
+      <div data-testid='overall-time' style={{ color: 'var(--color-fg-subtle)', marginRight: '10px' }}>{new Date(report.startTime).toLocaleString()}</div>
+      <div data-testid='overall-duration' style={{ color: 'var(--color-fg-subtle)' }}>Total time: {msToString(report.duration)}</div>
     </div>
     {!!report.errors.length && <AutoChip header='Errors' dataTestId='report-errors'>
       {report.errors.map((error, index) => <TestErrorView key={'test-report-error-message-' + index} error={error}></TestErrorView>)}
diff --git a/packages/html-reporter/src/testResultView.tsx b/packages/html-reporter/src/testResultView.tsx
index bdaec18d24..8b95c02bdf 100644
--- a/packages/html-reporter/src/testResultView.tsx
+++ b/packages/html-reporter/src/testResultView.tsx
@@ -77,7 +77,7 @@ export const TestResultView: React.FC<{
   result: TestResult,
 }> = ({ test, result }) => {
   const { screenshots, videos, traces, otherAttachments, diffs, errors, otherAttachmentAnchors, screenshotAnchors } = React.useMemo(() => {
-    const attachments = result?.attachments || [];
+    const attachments = result.attachments;
     const screenshots = new Set(attachments.filter(a => a.contentType.startsWith('image/')));
     const screenshotAnchors = [...screenshots].map(a => `attachment-${a.name}`);
     const videos = attachments.filter(a => a.contentType.startsWith('video/'));
diff --git a/packages/playwright-core/src/browserServerImpl.ts b/packages/playwright-core/src/browserServerImpl.ts
index 73455aa5c0..80053db7a0 100644
--- a/packages/playwright-core/src/browserServerImpl.ts
+++ b/packages/playwright-core/src/browserServerImpl.ts
@@ -38,6 +38,7 @@ export class BrowserServerLauncherImpl implements BrowserServerLauncher {
   async launchServer(options: LaunchServerOptions = {}): Promise<BrowserServer> {
     const playwright = createPlaywright({ sdkLanguage: 'javascript', isServer: true });
     // TODO: enable socks proxy once ipv6 is supported.
+    // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
     const socksProxy = false ? new SocksProxy() : undefined;
     playwright.options.socksProxyPort = await socksProxy?.listen(0);
 
diff --git a/packages/playwright-core/src/client/browserContext.ts b/packages/playwright-core/src/client/browserContext.ts
index 28afee001e..e30461464e 100644
--- a/packages/playwright-core/src/client/browserContext.ts
+++ b/packages/playwright-core/src/client/browserContext.ts
@@ -116,9 +116,7 @@ export class BrowserContext extends ChannelOwner<channels.BrowserContextChannel>
       const pageObject = Page.from(page);
       const parsedError = parseError(error);
       this.emit(Events.BrowserContext.WebError, new WebError(pageObject, parsedError));
-      if (pageObject) {
-        pageObject.emit(Events.Page.PageError, parsedError);
-      }
+      pageObject.emit(Events.Page.PageError, parsedError);
     });
     this._channel.on('dialog', ({ dialog }) => {
       const dialogObject = Dialog.from(dialog);
diff --git a/packages/playwright-core/src/client/browserType.ts b/packages/playwright-core/src/client/browserType.ts
index d4eb59ff5a..a7ef63f855 100644
--- a/packages/playwright-core/src/client/browserType.ts
+++ b/packages/playwright-core/src/client/browserType.ts
@@ -150,7 +150,7 @@ export class BrowserType extends ChannelOwner<channels.BrowserTypeChannel> imple
       let closeError: string | undefined;
       const onPipeClosed = (reason?: string) => {
         // Emulate all pages, contexts and the browser closing upon disconnect.
-        for (const context of browser.contexts() || []) {
+        for (const context of browser.contexts()) {
           for (const page of context.pages()) {
             page._onClose();
           }
diff --git a/packages/playwright-core/src/client/connection.ts b/packages/playwright-core/src/client/connection.ts
index dba0cdd303..51394e6066 100644
--- a/packages/playwright-core/src/client/connection.ts
+++ b/packages/playwright-core/src/client/connection.ts
@@ -137,7 +137,7 @@ export class Connection extends EventEmitter {
     }
     const location = frames[0] ? { file: frames[0].file, line: frames[0].line, column: frames[0].column } : undefined;
     const metadata: channels.Metadata = { apiName, location, internal: !apiName, stepId };
-    if (this._tracingCount && frames && type !== 'LocalUtils') {
+    if (this._tracingCount && type !== 'LocalUtils') {
       this._localUtils?._channel.addStackToTracingNoReply({ callData: { stack: frames, id } }).catch(() => {});
     }
     // We need to exit zones before calling into the server, otherwise
@@ -217,7 +217,7 @@ export class Connection extends EventEmitter {
 
   private _tChannelImplFromWire(names: '*' | string[], arg: any, path: string, context: ValidatorContext) {
     if (arg && typeof arg === 'object' && typeof arg.guid === 'string') {
-      const object = this._objects.get(arg.guid)!;
+      const object = this._objects.get(arg.guid);
       if (!object) {
         throw new Error(`Object with guid ${arg.guid} was not bound in the connection`);
       }
diff --git a/packages/playwright-core/src/client/consoleMessage.ts b/packages/playwright-core/src/client/consoleMessage.ts
index fcdc3fd149..f880ff47a4 100644
--- a/packages/playwright-core/src/client/consoleMessage.ts
+++ b/packages/playwright-core/src/client/consoleMessage.ts
@@ -28,7 +28,7 @@ export class ConsoleMessage implements api.ConsoleMessage {
   private _event: channels.BrowserContextConsoleEvent | channels.ElectronApplicationConsoleEvent;
 
   constructor(event: channels.BrowserContextConsoleEvent | channels.ElectronApplicationConsoleEvent) {
-    this._page = ('page' in event && event.page) ? Page.from(event.page) : null;
+    this._page = 'page' in event ? Page.from(event.page) : null;
     this._event = event;
   }
 
diff --git a/packages/playwright-core/src/client/elementHandle.ts b/packages/playwright-core/src/client/elementHandle.ts
index c731781ffb..30387fb7c1 100644
--- a/packages/playwright-core/src/client/elementHandle.ts
+++ b/packages/playwright-core/src/client/elementHandle.ts
@@ -248,6 +248,7 @@ export function convertSelectOptionValues(values: string | api.ElementHandle | S
     return {};
   }
   for (let i = 0; i < values.length; i++) {
+    // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
     assert(values[i] !== null, `options[${i}]: expected object, got null`);
   }
   if (values[0] instanceof ElementHandle) {
@@ -262,6 +263,7 @@ export function convertSelectOptionValues(values: string | api.ElementHandle | S
 type SetInputFilesFiles = Pick<channels.ElementHandleSetInputFilesParams, 'payloads' | 'localPaths' | 'localDirectory' | 'streams' | 'directoryStream'>;
 
 function filePayloadExceedsSizeLimit(payloads: FilePayload[]) {
+  // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
   return payloads.reduce((size, item) => size + (item.buffer ? item.buffer.byteLength : 0), 0) >= fileUploadSizeLimit;
 }
 
diff --git a/packages/playwright-core/src/client/eventEmitter.ts b/packages/playwright-core/src/client/eventEmitter.ts
index 01d620225d..1bf502a15b 100644
--- a/packages/playwright-core/src/client/eventEmitter.ts
+++ b/packages/playwright-core/src/client/eventEmitter.ts
@@ -66,6 +66,7 @@ export class EventEmitter implements EventEmitterType {
     }
 
     const handler = events[type];
+    // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
     if (handler === undefined) {
       return false;
     }
@@ -120,6 +121,7 @@ export class EventEmitter implements EventEmitterType {
     } else {
       // To avoid recursion in the case that type === "newListener"! Before
       // adding it to the listeners, first emit "newListener".
+      // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
       if (events.newListener !== undefined) {
         this.emit('newListener', type, unwrapListener(listener));
 
@@ -194,6 +196,7 @@ export class EventEmitter implements EventEmitterType {
     }
 
     const list = events[type];
+    // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
     if (list === undefined) {
       return this;
     }
@@ -203,6 +206,7 @@ export class EventEmitter implements EventEmitterType {
         this._events = Object.create(null);
       } else {
         delete events[type];
+        // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
         if (events.removeListener) {
           this.emit('removeListener', type, (list as any).listener ?? listener);
         }
@@ -233,6 +237,7 @@ export class EventEmitter implements EventEmitterType {
         events[type] = list[0];
       }
 
+      // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
       if (events.removeListener !== undefined) {
         this.emit('removeListener', type, originalListener || listener);
       }
@@ -280,10 +285,12 @@ export class EventEmitter implements EventEmitterType {
     }
 
     // not listening for removeListener, no need to emit
+    // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
     if (!events.removeListener) {
       if (type === undefined) {
         this._events = Object.create(null);
         this._eventsCount = 0;
+        // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
       } else if (events[type] !== undefined) {
         if (--this._eventsCount === 0) {
           this._events = Object.create(null);
@@ -315,6 +322,7 @@ export class EventEmitter implements EventEmitterType {
 
     if (typeof listeners === 'function') {
       this.removeListener(type, listeners);
+      // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
     } else if (listeners !== undefined) {
       // LIFO order
       for (let i = listeners.length - 1; i >= 0; i--) {
@@ -338,6 +346,7 @@ export class EventEmitter implements EventEmitterType {
       if (typeof listener === 'function') {
         return 1;
       }
+      // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
       if (listener !== undefined) {
         return listener.length;
       }
@@ -370,6 +379,7 @@ export class EventEmitter implements EventEmitterType {
     }
 
     const listener = events[type];
+    // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
     if (listener === undefined) {
       return [];
     }
@@ -421,6 +431,6 @@ function unwrapListeners(arr: Listener[]): Listener[] {
   return arr.map(l => wrappedListener(l) ?? l);
 }
 
-function wrappedListener(l: Listener): Listener {
+function wrappedListener(l: Listener): Listener | undefined {
   return (l as any).listener;
 }
diff --git a/packages/playwright-core/src/client/fetch.ts b/packages/playwright-core/src/client/fetch.ts
index d508b6fd3a..2e60fd9933 100644
--- a/packages/playwright-core/src/client/fetch.ts
+++ b/packages/playwright-core/src/client/fetch.ts
@@ -206,6 +206,7 @@ export class APIRequestContext extends ChannelOwner<channels.APIRequestContextCh
           throw new Error(`Unexpected 'data' type`);
         }
       } else if (options.form) {
+        // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
         if (globalThis.FormData && options.form instanceof FormData) {
           formData = [];
           for (const [name, value] of options.form.entries()) {
@@ -219,6 +220,7 @@ export class APIRequestContext extends ChannelOwner<channels.APIRequestContextCh
         }
       } else if (options.multipart) {
         multipartData = [];
+        // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
         if (globalThis.FormData && options.multipart instanceof FormData) {
           const form = options.multipart;
           for (const [name, value] of form.entries()) {
diff --git a/packages/playwright-core/src/client/frame.ts b/packages/playwright-core/src/client/frame.ts
index c8c190cc8f..dac5058108 100644
--- a/packages/playwright-core/src/client/frame.ts
+++ b/packages/playwright-core/src/client/frame.ts
@@ -444,6 +444,7 @@ export class Frame extends ChannelOwner<channels.FrameChannel> implements api.Fr
 
   async waitForFunction<R, Arg>(pageFunction: structs.PageFunction<Arg, R>, arg?: Arg, options: WaitForFunctionOptions = {}): Promise<structs.SmartHandle<R>> {
     if (typeof options.polling === 'string') {
+      // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
       assert(options.polling === 'raf', 'Unknown polling option: ' + options.polling);
     }
     const result = await this._channel.waitForFunction({
diff --git a/packages/playwright-core/src/client/network.ts b/packages/playwright-core/src/client/network.ts
index 56e5e879bb..958ed06d9f 100644
--- a/packages/playwright-core/src/client/network.ts
+++ b/packages/playwright-core/src/client/network.ts
@@ -945,6 +945,7 @@ export class RawHeaders {
   static _fromHeadersObjectLossy(headers: Headers): RawHeaders {
     const headersArray: HeadersArray = Object.entries(headers).map(([name, value]) => ({
       name, value
+      // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
     })).filter(header => header.value !== undefined);
     return new RawHeaders(headersArray);
   }
@@ -958,7 +959,7 @@ export class RawHeaders {
 
   get(name: string): string | null {
     const values = this.getAll(name);
-    if (!values || !values.length) {
+    if (!values.length) {
       return null;
     }
     return values.join(name.toLowerCase() === 'set-cookie' ? '\n' : ', ');
diff --git a/packages/playwright-core/src/client/playwright.ts b/packages/playwright-core/src/client/playwright.ts
index 7221a04115..2590a5beb1 100644
--- a/packages/playwright-core/src/client/playwright.ts
+++ b/packages/playwright-core/src/client/playwright.ts
@@ -51,7 +51,7 @@ export class Playwright extends ChannelOwner<channels.PlaywrightChannel> {
     this._bidiChromium._playwright = this;
     this._bidiFirefox = BrowserType.from(initializer.bidiFirefox);
     this._bidiFirefox._playwright = this;
-    this.devices = this._connection.localUtils().devices ?? {};
+    this.devices = this._connection.localUtils().devices;
     this.selectors = new Selectors();
     this.errors = { TimeoutError };
 
diff --git a/packages/playwright-core/src/common/socksProxy.ts b/packages/playwright-core/src/common/socksProxy.ts
index 615d47eb11..7c3c0286af 100644
--- a/packages/playwright-core/src/common/socksProxy.ts
+++ b/packages/playwright-core/src/common/socksProxy.ts
@@ -200,7 +200,7 @@ class SocksConnection {
 
   private async _readBytes(length: number): Promise<Buffer> {
     this._fence = this._offset + length;
-    if (!this._buffer || this._buffer.length < this._fence) {
+    if (this._buffer.length < this._fence) {
       await new Promise<void>(f => this._fenceCallback = f);
     }
     this._offset += length;
diff --git a/packages/playwright-core/src/common/types.ts b/packages/playwright-core/src/common/types.ts
index 55145b5565..da62f3298c 100644
--- a/packages/playwright-core/src/common/types.ts
+++ b/packages/playwright-core/src/common/types.ts
@@ -20,4 +20,10 @@ export type Rect = Size & Point;
 export type Quad = [ Point, Point, Point, Point ];
 export type TimeoutOptions = { timeout?: number };
 export type NameValue = { name: string, value: string };
-export type HeadersArray = NameValue[];
\ No newline at end of file
+export type HeadersArray = NameValue[];
+
+export const assertUnreachable = (x: never): never => assertUnreachableWithError(x, new Error('Unreachable variant'));
+
+export const assertUnreachableWithError = (x: never, error: Error): never => {
+  throw error;
+};
\ No newline at end of file
diff --git a/packages/playwright-core/src/protocol/serializers.ts b/packages/playwright-core/src/protocol/serializers.ts
index 6794d20797..78f47dfdf3 100644
--- a/packages/playwright-core/src/protocol/serializers.ts
+++ b/packages/playwright-core/src/protocol/serializers.ts
@@ -15,6 +15,7 @@
  */
 
 import type { SerializedValue } from '@protocol/channels';
+import { assertUnreachable } from '../common/types';
 
 export function parseSerializedValue(value: SerializedValue, handles: any[] | undefined): any {
   return innerParseSerializedValue(value, handles, new Map());
@@ -34,23 +35,28 @@ function innerParseSerializedValue(value: SerializedValue, handles: any[] | unde
     return value.b;
   }
   if (value.v !== undefined) {
-    if (value.v === 'undefined') {
-      return undefined;
-    }
-    if (value.v === 'null') {
-      return null;
-    }
-    if (value.v === 'NaN') {
-      return NaN;
-    }
-    if (value.v === 'Infinity') {
-      return Infinity;
-    }
-    if (value.v === '-Infinity') {
-      return -Infinity;
-    }
-    if (value.v === '-0') {
-      return -0;
+    switch (value.v) {
+      case 'undefined': {
+        return undefined;
+      }
+      case 'null': {
+        return null;
+      }
+      case 'NaN': {
+        return NaN;
+      }
+      case 'Infinity': {
+        return Infinity;
+      }
+      case '-Infinity': {
+        return -Infinity;
+      }
+      case '-0': {
+        return -0;
+      }
+      default: {
+        return assertUnreachable(value.v);
+      }
     }
   }
   if (value.d !== undefined) {
diff --git a/packages/playwright-core/src/protocol/transport.ts b/packages/playwright-core/src/protocol/transport.ts
index ad8fdd29d0..e5c0913b30 100644
--- a/packages/playwright-core/src/protocol/transport.ts
+++ b/packages/playwright-core/src/protocol/transport.ts
@@ -79,6 +79,7 @@ export class PipeTransport {
 
   _dispatch(buffer: Buffer) {
     this._data = Buffer.concat([this._data, buffer]);
+    // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
     while (true) {
       if (!this._bytesLeft && this._data.length < 4) {
         // Need more data.
diff --git a/packages/playwright-core/src/protocol/validatorPrimitives.ts b/packages/playwright-core/src/protocol/validatorPrimitives.ts
index 6c66e153d4..32fcb58046 100644
--- a/packages/playwright-core/src/protocol/validatorPrimitives.ts
+++ b/packages/playwright-core/src/protocol/validatorPrimitives.ts
@@ -14,6 +14,7 @@
  * limitations under the License.
  */
 
+import { assertUnreachableWithError } from '../common/types';
 import { isUnderTest } from '../utils';
 
 export class ValidationError extends Error {}
@@ -67,28 +68,32 @@ export const tString: Validator = (arg: any, path: string, context: ValidatorCon
   throw new ValidationError(`${path}: expected string, got ${typeof arg}`);
 };
 export const tBinary: Validator = (arg: any, path: string, context: ValidatorContext) => {
-  if (context.binary === 'fromBase64') {
-    if (arg instanceof String) {
-      return Buffer.from(arg.valueOf(), 'base64');
+  switch (context.binary) {
+    case 'fromBase64': {
+      if (arg instanceof String) {
+        return Buffer.from(arg.valueOf(), 'base64');
+      }
+      if (typeof arg === 'string') {
+        return Buffer.from(arg, 'base64');
+      }
+      throw new ValidationError(`${path}: expected base64-encoded buffer, got ${typeof arg}`);
     }
-    if (typeof arg === 'string') {
-      return Buffer.from(arg, 'base64');
+    case 'toBase64': {
+      if (!(arg instanceof Buffer)) {
+        throw new ValidationError(`${path}: expected Buffer, got ${typeof arg}`);
+      }
+      return (arg as Buffer).toString('base64');
+    }
+    case 'buffer': {
+      if (!(arg instanceof Buffer)) {
+        throw new ValidationError(`${path}: expected Buffer, got ${typeof arg}`);
+      }
+      return arg;
+    }
+    default: {
+      return assertUnreachableWithError(context.binary, new ValidationError(`Unsupported binary behavior "${context.binary}"`));
     }
-    throw new ValidationError(`${path}: expected base64-encoded buffer, got ${typeof arg}`);
   }
-  if (context.binary === 'toBase64') {
-    if (!(arg instanceof Buffer)) {
-      throw new ValidationError(`${path}: expected Buffer, got ${typeof arg}`);
-    }
-    return (arg as Buffer).toString('base64');
-  }
-  if (context.binary === 'buffer') {
-    if (!(arg instanceof Buffer)) {
-      throw new ValidationError(`${path}: expected Buffer, got ${typeof arg}`);
-    }
-    return arg;
-  }
-  throw new ValidationError(`Unsupported binary behavior "${context.binary}"`);
 };
 export const tUndefined: Validator = (arg: any, path: string, context: ValidatorContext) => {
   if (Object.is(arg, undefined)) {
@@ -156,6 +161,7 @@ export const tChannel = (names: '*' | string[]): Validator => {
 export const tType = (name: string): Validator => {
   return (arg: any, path: string, context: ValidatorContext) => {
     const v = scheme[name];
+    // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
     if (!v) {
       throw new ValidationError(path + ': unknown type "' + name + '"');
     }
diff --git a/packages/playwright-core/src/remote/playwrightConnection.ts b/packages/playwright-core/src/remote/playwrightConnection.ts
index 3b10592d9d..0a6f8c1cc4 100644
--- a/packages/playwright-core/src/remote/playwrightConnection.ts
+++ b/packages/playwright-core/src/remote/playwrightConnection.ts
@@ -28,6 +28,7 @@ import { DebugControllerDispatcher } from '../server/dispatchers/debugController
 import { startProfiling, stopProfiling } from '../utils';
 import { monotonicTime } from '../utils';
 import { debugLogger } from '../utils/debugLogger';
+import { assertUnreachableWithError } from '../common/types';
 
 export type ClientType = 'controller' | 'launch-browser' | 'reuse-browser' | 'pre-launched-browser-or-android';
 
@@ -108,16 +109,20 @@ export class PlaywrightConnection {
 
     this._root = new RootDispatcher(this._dispatcherConnection, async (scope, options) => {
       await startProfiling();
-      if (clientType === 'reuse-browser') {
-        return await this._initReuseBrowsersMode(scope);
+      switch (clientType) {
+        case 'reuse-browser': {
+          return await this._initReuseBrowsersMode(scope);
+        }
+        case 'pre-launched-browser-or-android': {
+          return this._preLaunched.browser ? await this._initPreLaunchedBrowserMode(scope) : await this._initPreLaunchedAndroidMode(scope);
+        }
+        case 'launch-browser': {
+          return await this._initLaunchBrowserMode(scope, options);
+        }
+        default: {
+          return assertUnreachableWithError(clientType, new Error('Unsupported client type: ' + clientType));
+        }
       }
-      if (clientType === 'pre-launched-browser-or-android') {
-        return this._preLaunched.browser ? await this._initPreLaunchedBrowserMode(scope) : await this._initPreLaunchedAndroidMode(scope);
-      }
-      if (clientType === 'launch-browser') {
-        return await this._initLaunchBrowserMode(scope, options);
-      }
-      throw new Error('Unsupported client type: ' + clientType);
     });
   }
 
@@ -233,9 +238,6 @@ export class PlaywrightConnection {
             await context.stopPendingOperations('Connection closed');
           }
         }
-        if (!browser.contexts()) {
-          await browser.close({ reason: 'Connection terminated' });
-        }
       }
     });
 
diff --git a/packages/playwright-core/src/server/android/android.ts b/packages/playwright-core/src/server/android/android.ts
index e0e437ab26..9c7035d7da 100644
--- a/packages/playwright-core/src/server/android/android.ts
+++ b/packages/playwright-core/src/server/android/android.ts
@@ -334,7 +334,7 @@ export class AndroidDevice extends SdkObject {
     const artifactsDir = await fs.promises.mkdtemp(ARTIFACTS_FOLDER);
     const cleanupArtifactsDir = async () => {
       const errors = await removeFolders([artifactsDir]);
-      for (let i = 0; i < (errors || []).length; ++i) {
+      for (let i = 0; i < errors.length; ++i) {
         debug('pw:android')(`exception while removing ${artifactsDir}: ${errors[i]}`);
       }
     };
@@ -438,6 +438,7 @@ export class AndroidDevice extends SdkObject {
       }
 
       const pkg = await this._extractPkg(pid);
+      // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
       if (this._isClosed) {
         return;
       }
diff --git a/packages/playwright-core/src/server/bidi/bidiBrowser.ts b/packages/playwright-core/src/server/bidi/bidiBrowser.ts
index 569998b115..a314127510 100644
--- a/packages/playwright-core/src/server/bidi/bidiBrowser.ts
+++ b/packages/playwright-core/src/server/bidi/bidiBrowser.ts
@@ -159,9 +159,9 @@ export class BidiBrowser extends Browser {
       }
       return;
     }
-    let context = this._contexts.get(event.userContext);
+    let context: BidiBrowserContext | undefined | null = this._contexts.get(event.userContext);
     if (!context) {
-      context = this._defaultContext as BidiBrowserContext;
+      context = this._defaultContext as BidiBrowserContext | null;
     }
     if (!context) {
       return;
@@ -240,6 +240,7 @@ export class BidiBrowserContext extends BrowserContext {
         httpOnly: c.httpOnly,
         secure: c.secure,
         expires: c.expiry ?? -1,
+        // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
         sameSite: c.sameSite ? fromBidiSameSite(c.sameSite) : 'None',
       };
       return copy;
diff --git a/packages/playwright-core/src/server/bidi/bidiExecutionContext.ts b/packages/playwright-core/src/server/bidi/bidiExecutionContext.ts
index cfc691f52e..1d063f6e6e 100644
--- a/packages/playwright-core/src/server/bidi/bidiExecutionContext.ts
+++ b/packages/playwright-core/src/server/bidi/bidiExecutionContext.ts
@@ -14,6 +14,7 @@
  * limitations under the License.
  */
 
+import { assertUnreachableWithError } from 'playwright-core/lib/common/types';
 import { parseEvaluationResultValue } from '../isomorphic/utilityScriptSerializers';
 import * as js from '../javascript';
 import type { BidiSession } from './bidiConnection';
@@ -51,13 +52,17 @@ export class BidiExecutionContext implements js.ExecutionContextDelegate {
       awaitPromise: true,
       userActivation: true,
     });
-    if (response.type === 'success') {
-      return BidiDeserializer.deserialize(response.result);
+    switch (response.type) {
+      case 'success': {
+        return BidiDeserializer.deserialize(response.result);
+      }
+      case 'exception': {
+        throw new js.JavaScriptErrorInEvaluate(response.exceptionDetails.text + '\nFull val: ' + JSON.stringify(response.exceptionDetails));
+      }
+      default: {
+        return assertUnreachableWithError(response, new js.JavaScriptErrorInEvaluate('Unexpected response type: ' + JSON.stringify(response)));
+      }
     }
-    if (response.type === 'exception') {
-      throw new js.JavaScriptErrorInEvaluate(response.exceptionDetails.text + '\nFull val: ' + JSON.stringify(response.exceptionDetails));
-    }
-    throw new js.JavaScriptErrorInEvaluate('Unexpected response type: ' + JSON.stringify(response));
   }
 
   async rawEvaluateHandle(expression: string): Promise<js.ObjectId> {
@@ -69,16 +74,20 @@ export class BidiExecutionContext implements js.ExecutionContextDelegate {
       awaitPromise: true,
       userActivation: true,
     });
-    if (response.type === 'success') {
-      if ('handle' in response.result) {
-        return response.result.handle!;
+    switch (response.type) {
+      case 'success': {
+        if ('handle' in response.result) {
+          return response.result.handle!;
+        }
+        throw new js.JavaScriptErrorInEvaluate('Cannot get handle: ' + JSON.stringify(response.result));
+      }
+      case 'exception': {
+        throw new js.JavaScriptErrorInEvaluate(response.exceptionDetails.text + '\nFull val: ' + JSON.stringify(response.exceptionDetails));
+      }
+      default: {
+        return assertUnreachableWithError(response, new js.JavaScriptErrorInEvaluate('Unexpected response type: ' + JSON.stringify(response)));
       }
-      throw new js.JavaScriptErrorInEvaluate('Cannot get handle: ' + JSON.stringify(response.result));
     }
-    if (response.type === 'exception') {
-      throw new js.JavaScriptErrorInEvaluate(response.exceptionDetails.text + '\nFull val: ' + JSON.stringify(response.exceptionDetails));
-    }
-    throw new js.JavaScriptErrorInEvaluate('Unexpected response type: ' + JSON.stringify(response));
   }
 
   async evaluateWithArguments(functionDeclaration: string, returnByValue: boolean, utilityScript: js.JSHandle<any>, values: any[], objectIds: string[]): Promise<any> {
@@ -95,17 +104,21 @@ export class BidiExecutionContext implements js.ExecutionContextDelegate {
       awaitPromise: true,
       userActivation: true,
     });
-    if (response.type === 'exception') {
-      throw new js.JavaScriptErrorInEvaluate(response.exceptionDetails.text + '\nFull val: ' + JSON.stringify(response.exceptionDetails));
-    }
-    if (response.type === 'success') {
-      if (returnByValue) {
-        return parseEvaluationResultValue(BidiDeserializer.deserialize(response.result));
+    switch (response.type) {
+      case 'success': {
+        if (returnByValue) {
+          return parseEvaluationResultValue(BidiDeserializer.deserialize(response.result));
+        }
+        const objectId = 'handle' in response.result ? response.result.handle : undefined ;
+        return utilityScript._context.createHandle({ objectId, ...response.result });
+      }
+      case 'exception': {
+        throw new js.JavaScriptErrorInEvaluate(response.exceptionDetails.text + '\nFull val: ' + JSON.stringify(response.exceptionDetails));
+      }
+      default: {
+        return assertUnreachableWithError(response, new js.JavaScriptErrorInEvaluate('Unexpected response type: ' + JSON.stringify(response)));
       }
-      const objectId = 'handle' in response.result ? response.result.handle : undefined ;
-      return utilityScript._context.createHandle({ objectId, ...response.result });
     }
-    throw new js.JavaScriptErrorInEvaluate('Unexpected response type: ' + JSON.stringify(response));
   }
 
   async getProperties(context: js.ExecutionContext, objectId: js.ObjectId): Promise<Map<string, js.JSHandle>> {
@@ -134,13 +147,17 @@ export class BidiExecutionContext implements js.ExecutionContextDelegate {
       awaitPromise: true,
       userActivation: true,
     });
-    if (response.type === 'exception') {
-      throw new js.JavaScriptErrorInEvaluate(response.exceptionDetails.text + '\nFull val: ' + JSON.stringify(response.exceptionDetails));
+    switch (response.type) {
+      case 'success': {
+        return response.result;
+      }
+      case 'exception': {
+        throw new js.JavaScriptErrorInEvaluate(response.exceptionDetails.text + '\nFull val: ' + JSON.stringify(response.exceptionDetails));
+      }
+      default: {
+        return assertUnreachableWithError(response, new js.JavaScriptErrorInEvaluate('Unexpected response type: ' + JSON.stringify(response)));
+      }
     }
-    if (response.type === 'success') {
-      return response.result;
-    }
-    throw new js.JavaScriptErrorInEvaluate('Unexpected response type: ' + JSON.stringify(response));
   }
 }
 
diff --git a/packages/playwright-core/src/server/bidi/bidiNetworkManager.ts b/packages/playwright-core/src/server/bidi/bidiNetworkManager.ts
index 465e51e081..8fbbc02d78 100644
--- a/packages/playwright-core/src/server/bidi/bidiNetworkManager.ts
+++ b/packages/playwright-core/src/server/bidi/bidiNetworkManager.ts
@@ -272,6 +272,7 @@ class BidiRouteImpl implements network.RouteDelegate {
   async continue(overrides: types.NormalizedContinueOverrides) {
     // Firefox does not update content-length header.
     let headers = overrides.headers || this._request.headers();
+    // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
     if (overrides.postData && headers) {
       headers = headers.map(header => {
         if (header.name.toLowerCase() === 'content-length') {
@@ -342,14 +343,17 @@ function toBidiHeaders(headers: types.HeadersArray): bidi.Network.Header[] {
 }
 
 export function bidiBytesValueToString(value: bidi.Network.BytesValue): string {
-  if (value.type === 'string') {
-    return value.value;
+  switch (value.type) {
+    case 'string': {
+      return value.value;
+    }
+    case 'base64': {
+      return Buffer.from(value.type, 'base64').toString('binary');
+    }
+    default: {
+      return 'unknown value type: ' + (value as any).type;
+    }
   }
-  if (value.type === 'base64') {
-    return Buffer.from(value.type, 'base64').toString('binary');
-  }
-  return 'unknown value type: ' + (value as any).type;
-
 }
 
 function toBidiSameSite(sameSite?: 'Strict' | 'Lax' | 'None'): bidi.Network.SameSite | undefined {
diff --git a/packages/playwright-core/src/server/bidi/bidiPage.ts b/packages/playwright-core/src/server/bidi/bidiPage.ts
index b25a4711ff..5d4f483079 100644
--- a/packages/playwright-core/src/server/bidi/bidiPage.ts
+++ b/packages/playwright-core/src/server/bidi/bidiPage.ts
@@ -189,7 +189,7 @@ export class BidiPage implements PageDelegate {
     if (url.startsWith('file:') || url.startsWith('data:') || url === 'about:blank') {
       // Navigation to file urls doesn't emit network events, so we fire 'commit' event right when navigation is started.
       // Doing it in domcontentload would be too late as we'd clear frame tree.
-      const frame = this._page._frameManager.frame(frameId)!;
+      const frame = this._page._frameManager.frame(frameId);
       if (frame) {
         this._page._frameManager.frameCommittedNewDocumentNavigation(frameId, params.url, '', params.navigation!, /* initial */ false);
       }
@@ -514,6 +514,7 @@ export class BidiPage implements PageDelegate {
         return 'error:notconnected';
       }
       const rects = node.getClientRects();
+      // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
       if (!rects) {
         return null;
       }
diff --git a/packages/playwright-core/src/server/bidi/third_party/bidiDeserializer.ts b/packages/playwright-core/src/server/bidi/third_party/bidiDeserializer.ts
index 4bdb3d081c..986fd7a84c 100644
--- a/packages/playwright-core/src/server/bidi/third_party/bidiDeserializer.ts
+++ b/packages/playwright-core/src/server/bidi/third_party/bidiDeserializer.ts
@@ -15,6 +15,7 @@ import type * as Bidi from './bidiProtocol';
  */
 export class BidiDeserializer {
   static deserialize(result: Bidi.Script.RemoteValue): any {
+    // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
     if (!result) {
       return undefined;
     }
diff --git a/packages/playwright-core/src/server/browserContext.ts b/packages/playwright-core/src/server/browserContext.ts
index 32f4efaa99..7a020fdac1 100644
--- a/packages/playwright-core/src/server/browserContext.ts
+++ b/packages/playwright-core/src/server/browserContext.ts
@@ -215,7 +215,7 @@ export abstract class BrowserContext extends SdkObject {
     await this._cancelAllRoutesInFlight();
 
     // Close extra pages early.
-    let page: Page | undefined = this.pages()[0];
+    let page = this.pages()[0] as Page | undefined;
     const [, ...otherPages] = this.pages();
     for (const p of otherPages) {
       await p.close(metadata);
@@ -391,7 +391,7 @@ export abstract class BrowserContext extends SdkObject {
       // Race against BrowserContext.close
       await Promise.race([waitForEvent.promise, this._closePromise]);
     }
-    const page = this.possiblyUninitializedPages()[0];
+    const page = this.possiblyUninitializedPages()[0] as Page | undefined;
     if (!page) {
       return;
     }
@@ -593,7 +593,7 @@ export abstract class BrowserContext extends SdkObject {
     if (!oldOrigins.size && !newOrigins.size) {
       return;
     }
-    let page = this.pages()[0];
+    let page = this.pages()[0] as Page | undefined;
 
     const internalMetadata = serverSideCallMetadata();
     page = page || await this.newPage({
diff --git a/packages/playwright-core/src/server/chromium/chromium.ts b/packages/playwright-core/src/server/chromium/chromium.ts
index 7ac9c6f8be..e2cb848ae2 100644
--- a/packages/playwright-core/src/server/chromium/chromium.ts
+++ b/packages/playwright-core/src/server/chromium/chromium.ts
@@ -79,7 +79,7 @@ export class Chromium extends BrowserType {
 
     if (!headersMap) {
       headersMap = { 'User-Agent': getUserAgent() };
-    } else if (headersMap && !Object.keys(headersMap).some(key => key.toLowerCase() === 'user-agent')) {
+    } else if (!Object.keys(headersMap).some(key => key.toLowerCase() === 'user-agent')) {
       headersMap['User-Agent'] = getUserAgent();
     }
 
diff --git a/packages/playwright-core/src/server/chromium/crBrowser.ts b/packages/playwright-core/src/server/chromium/crBrowser.ts
index 397725e34a..d66c15a232 100644
--- a/packages/playwright-core/src/server/chromium/crBrowser.ts
+++ b/packages/playwright-core/src/server/chromium/crBrowser.ts
@@ -164,7 +164,7 @@ export class CRBrowser extends Browser {
     if (!context) {
       // TODO: auto attach only to pages from our contexts.
       // assert(this._defaultContext);
-      context = this._defaultContext as CRBrowserContext;
+      context = this._defaultContext as CRBrowserContext | null;
     }
 
     if (targetInfo.type === 'other' && targetInfo.url.startsWith('devtools://devtools') && this._devtools) {
diff --git a/packages/playwright-core/src/server/chromium/crNetworkManager.ts b/packages/playwright-core/src/server/chromium/crNetworkManager.ts
index 955f7e7b5f..046d8aaf82 100644
--- a/packages/playwright-core/src/server/chromium/crNetworkManager.ts
+++ b/packages/playwright-core/src/server/chromium/crNetworkManager.ts
@@ -416,7 +416,7 @@ requestPausedSessionInfo!.session._sendMayFail('Fetch.continueRequest', { reques
       }
       return Buffer.concat(chunks);
     };
-    const timingPayload = responsePayload.timing!;
+    const timingPayload = responsePayload.timing;
     let timing: network.ResourceTiming;
     if (timingPayload && !this._responseExtraInfoTracker.servedFromCache(request._requestId)) {
       timing = {
@@ -828,7 +828,7 @@ class ResponseExtraInfoTracker {
   }
 
   private _patchHeaders(info: RequestInfo, index: number) {
-    const response = info.responses[index];
+    const response = info.responses[index] as network.Response | undefined;
     const requestExtraInfo = info.requestWillBeSentExtraInfo[index];
     if (response && requestExtraInfo) {
       response.request().setRawRequestHeaders(headersObjectToArray(requestExtraInfo.headers, '\n'));
diff --git a/packages/playwright-core/src/server/chromium/crPage.ts b/packages/playwright-core/src/server/chromium/crPage.ts
index 5346798870..f485f37008 100644
--- a/packages/playwright-core/src/server/chromium/crPage.ts
+++ b/packages/playwright-core/src/server/chromium/crPage.ts
@@ -212,7 +212,7 @@ export class CRPage implements PageDelegate {
 
   private async _go(delta: number): Promise<boolean> {
     const history = await this._mainFrameSession._client.send('Page.getNavigationHistory');
-    const entry = history.entries[history.currentIndex + delta];
+    const entry = history.entries[history.currentIndex + delta] as Protocol.Page.NavigationEntry | undefined;
     if (!entry) {
       return false;
     }
@@ -639,6 +639,7 @@ class FrameSession {
     // In this case, we already have a new session for this frame, so events
     // in the old session should be ignored.
     const session = this._crPage._sessionForFrame(frame);
+    // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
     return session && session !== this && !session._swappedIn;
   }
 
@@ -1140,6 +1141,7 @@ class FrameSession {
     const nodeInfo = await this._client.send('DOM.describeNode', {
       objectId: handle._objectId
     });
+    // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
     if (!nodeInfo || typeof nodeInfo.node.frameId !== 'string') {
       return null;
     }
@@ -1150,11 +1152,13 @@ class FrameSession {
     // document.documentElement has frameId of the owner frame.
     const documentElement = await handle.evaluateHandle(node => {
       const doc = node as Document;
+      // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
       if (doc.documentElement && doc.documentElement.ownerDocument === doc) {
         return doc.documentElement;
       }
       return node.ownerDocument ? node.ownerDocument.documentElement : null;
     });
+    // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
     if (!documentElement) {
       return null;
     }
@@ -1164,6 +1168,7 @@ class FrameSession {
     const nodeInfo = await this._client.send('DOM.describeNode', {
       objectId: documentElement._objectId
     });
+    // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
     const frameId = nodeInfo && typeof nodeInfo.node.frameId === 'string' ?
       nodeInfo.node.frameId : null;
     documentElement.dispose();
diff --git a/packages/playwright-core/src/server/codegen/csharp.ts b/packages/playwright-core/src/server/codegen/csharp.ts
index 80a0c75304..b01beb2d2d 100644
--- a/packages/playwright-core/src/server/codegen/csharp.ts
+++ b/packages/playwright-core/src/server/codegen/csharp.ts
@@ -37,6 +37,7 @@ export class CSharpLanguageGenerator implements LanguageGenerator {
     } else if (mode === 'mstest') {
       this.name = 'MSTest';
       this.id = 'csharp-mstest';
+      // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
     } else if (mode === 'nunit') {
       this.name = 'NUnit';
       this.id = 'csharp-nunit';
diff --git a/packages/playwright-core/src/server/codegen/java.ts b/packages/playwright-core/src/server/codegen/java.ts
index 7b466049d6..51d7e1244a 100644
--- a/packages/playwright-core/src/server/codegen/java.ts
+++ b/packages/playwright-core/src/server/codegen/java.ts
@@ -36,6 +36,7 @@ export class JavaLanguageGenerator implements LanguageGenerator {
     if (mode === 'library') {
       this.name = 'Library';
       this.id = 'java';
+      // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
     } else if (mode === 'junit') {
       this.name = 'JUnit';
       this.id = 'java-junit';
diff --git a/packages/playwright-core/src/server/debugController.ts b/packages/playwright-core/src/server/debugController.ts
index ac6d6ac4f3..3169d2b06c 100644
--- a/packages/playwright-core/src/server/debugController.ts
+++ b/packages/playwright-core/src/server/debugController.ts
@@ -240,9 +240,6 @@ export class DebugController extends SdkObject {
           await context.close({ reason: 'Browser collected' });
         }
       }
-      if (!browser.contexts()) {
-        await browser.close({ reason: 'Browser collected' });
-      }
     }
   }
 }
diff --git a/packages/playwright-core/src/server/dispatchers/artifactDispatcher.ts b/packages/playwright-core/src/server/dispatchers/artifactDispatcher.ts
index 2140c4bbdb..1a89706c89 100644
--- a/packages/playwright-core/src/server/dispatchers/artifactDispatcher.ts
+++ b/packages/playwright-core/src/server/dispatchers/artifactDispatcher.ts
@@ -31,6 +31,7 @@ export class ArtifactDispatcher extends Dispatcher<Artifact, channels.ArtifactCh
   }
 
   static fromNullable(parentScope: DispatcherScope, artifact: Artifact): ArtifactDispatcher | undefined {
+    // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
     if (!artifact) {
       return undefined;
     }
diff --git a/packages/playwright-core/src/server/dispatchers/browserContextDispatcher.ts b/packages/playwright-core/src/server/dispatchers/browserContextDispatcher.ts
index 2d77c77100..b59a3fe03e 100644
--- a/packages/playwright-core/src/server/dispatchers/browserContextDispatcher.ts
+++ b/packages/playwright-core/src/server/dispatchers/browserContextDispatcher.ts
@@ -350,6 +350,7 @@ export class BrowserContextDispatcher extends Dispatcher<BrowserContext, channel
 
   async harExport(params: channels.BrowserContextHarExportParams): Promise<channels.BrowserContextHarExportResult> {
     const artifact = await this._context._harExport(params.harId);
+    // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
     if (!artifact) {
       throw new Error('No HAR artifact. Ensure record.harPath is set.');
     }
diff --git a/packages/playwright-core/src/server/dispatchers/localUtilsDispatcher.ts b/packages/playwright-core/src/server/dispatchers/localUtilsDispatcher.ts
index 0bfa9a17b1..c4a71a9dc4 100644
--- a/packages/playwright-core/src/server/dispatchers/localUtilsDispatcher.ts
+++ b/packages/playwright-core/src/server/dispatchers/localUtilsDispatcher.ts
@@ -357,6 +357,7 @@ class HarBackend {
   private async _harFindResponse(url: string, method: string, headers: HeadersArray, postData: Buffer | undefined): Promise<har.Entry | undefined> {
     const harLog = this._harFile.log;
     const visited = new Set<har.Entry>();
+    // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
     while (true) {
       const entries: har.Entry[] = [];
       for (const candidate of harLog.entries) {
diff --git a/packages/playwright-core/src/server/dispatchers/webSocketRouteDispatcher.ts b/packages/playwright-core/src/server/dispatchers/webSocketRouteDispatcher.ts
index 48af5fe876..54a455ec2f 100644
--- a/packages/playwright-core/src/server/dispatchers/webSocketRouteDispatcher.ts
+++ b/packages/playwright-core/src/server/dispatchers/webSocketRouteDispatcher.ts
@@ -154,6 +154,7 @@ export class WebSocketRouteDispatcher extends Dispatcher<{ guid: string }, chann
 }
 
 function matchesPattern(dispatcher: PageDispatcher | BrowserContextDispatcher, baseURL: string | undefined, url: string) {
+  // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
   for (const pattern of dispatcher._webSocketInterceptionPatterns || []) {
     const urlMatch = pattern.regexSource ? new RegExp(pattern.regexSource, pattern.regexFlags) : pattern.glob;
     if (urlMatches(baseURL, url, urlMatch)) {
diff --git a/packages/playwright-core/src/server/dom.ts b/packages/playwright-core/src/server/dom.ts
index 0f59c21d73..cf9366d8c1 100644
--- a/packages/playwright-core/src/server/dom.ts
+++ b/packages/playwright-core/src/server/dom.ts
@@ -183,6 +183,7 @@ export class ElementHandle<T extends Node = Node> extends js.JSHandle<T> {
   }
 
   async isIframeElement(): Promise<boolean | 'error:notconnected'> {
+    // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
     return this.evaluateInUtility(([injected, node]) => node && (node.nodeName === 'IFRAME' || node.nodeName === 'FRAME'), {});
   }
 
@@ -497,6 +498,7 @@ export class ElementHandle<T extends Node = Node> extends js.JSHandle<T> {
       }
       progress.throwIfAborted();  // Avoid action that has side-effects.
       let restoreModifiers: types.KeyboardModifier[] | undefined;
+      // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
       if (options && options.modifiers) {
         restoreModifiers = await this._page.keyboard.ensureModifiers(options.modifiers);
       }
diff --git a/packages/playwright-core/src/server/fetch.ts b/packages/playwright-core/src/server/fetch.ts
index a8aa2adbef..2e77a38c35 100644
--- a/packages/playwright-core/src/server/fetch.ts
+++ b/packages/playwright-core/src/server/fetch.ts
@@ -566,6 +566,7 @@ export abstract class APIRequestContext extends SdkObject {
 
 
       progress.log(`→ ${options.method} ${url.toString()}`);
+      // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
       if (options.headers) {
         for (const [name, value] of Object.entries(options.headers)) {
           progress.log(`  ${name}: ${value}`);
diff --git a/packages/playwright-core/src/server/firefox/ffBrowser.ts b/packages/playwright-core/src/server/firefox/ffBrowser.ts
index 0da66ea2da..1a8edeefc7 100644
--- a/packages/playwright-core/src/server/firefox/ffBrowser.ts
+++ b/packages/playwright-core/src/server/firefox/ffBrowser.ts
@@ -123,6 +123,7 @@ export class FFBrowser extends Browser {
 
   _onAttachedToTarget(payload: Protocol.Browser.attachedToTargetPayload) {
     const { targetId, browserContextId, openerId, type } = payload.targetInfo;
+    // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
     assert(type === 'page');
     const context = browserContextId ? this._contexts.get(browserContextId)! : this._defaultContext as FFBrowserContext;
     assert(context, `Unknown context id:${browserContextId}, _defaultContext: ${this._defaultContext}`);
diff --git a/packages/playwright-core/src/server/firefox/ffInput.ts b/packages/playwright-core/src/server/firefox/ffInput.ts
index 05168ecfdb..4c13a17565 100644
--- a/packages/playwright-core/src/server/firefox/ffInput.ts
+++ b/packages/playwright-core/src/server/firefox/ffInput.ts
@@ -38,16 +38,20 @@ function toModifiersMask(modifiers: Set<types.KeyboardModifier>): number {
 }
 
 function toButtonNumber(button: types.MouseButton): number {
-  if (button === 'left') {
-    return 0;
+  switch (button) {
+    case 'left': {
+      return 0;
+    }
+    case 'middle': {
+      return 1;
+    }
+    case 'right': {
+      return 2;
+    }
+    default: {
+      return 0;
+    }
   }
-  if (button === 'middle') {
-    return 1;
-  }
-  if (button === 'right') {
-    return 2;
-  }
-  return 0;
 }
 
 function toButtonsMask(buttons: Set<types.MouseButton>): number {
diff --git a/packages/playwright-core/src/server/frameSelectors.ts b/packages/playwright-core/src/server/frameSelectors.ts
index 3497d4a7ca..e5223c2474 100644
--- a/packages/playwright-core/src/server/frameSelectors.ts
+++ b/packages/playwright-core/src/server/frameSelectors.ts
@@ -103,7 +103,7 @@ export class FrameSelectors {
     const targetContext = await resolved.frame._mainContext();
     const result: Promise<ElementHandle<Element>>[] = [];
     for (const property of properties.values()) {
-      const elementHandle = property.asElement() as ElementHandle<Element>;
+      const elementHandle = property.asElement() as ElementHandle<Element> | null;
       if (elementHandle) {
         result.push(adoptIfNeeded(elementHandle, targetContext));
       } else {
diff --git a/packages/playwright-core/src/server/frames.ts b/packages/playwright-core/src/server/frames.ts
index b212e2b2ae..042f07c544 100644
--- a/packages/playwright-core/src/server/frames.ts
+++ b/packages/playwright-core/src/server/frames.ts
@@ -107,6 +107,7 @@ export class FrameManager {
   }
 
   createDummyMainFrameIfNeeded() {
+    // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
     if (!this._mainFrame) {
       this.frameAttached(kDummyFrameId, null);
     }
@@ -143,6 +144,7 @@ export class FrameManager {
   frameAttached(frameId: string, parentFrameId: string | null | undefined): Frame {
     const parentFrame = parentFrameId ? this._frames.get(parentFrameId)! : null;
     if (!parentFrame) {
+      // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
       if (this._mainFrame) {
         // Update frame id to retain frame identity on cross-process navigation.
         this._frames.delete(this._mainFrame._id);
@@ -880,7 +882,7 @@ export class Frame extends SdkObject {
           throw injected.createStacklessError('Element is not attached to the DOM');
         }
         const elements = injected.querySelectorAll(info.parsed, root || document);
-        const element: Element | undefined  = elements[0];
+        const element  = elements[0] as Element | undefined;
         const visible = element ? injected.utils.isElementVisible(element) : false;
         let log = '';
         if (elements.length > 1) {
@@ -970,6 +972,7 @@ export class Frame extends SdkObject {
         if (document.doctype) {
           retVal = new XMLSerializer().serializeToString(document.doctype);
         }
+        // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
         if (document.documentElement) {
           retVal += document.documentElement.outerHTML;
         }
@@ -1083,6 +1086,7 @@ export class Frame extends SdkObject {
       let error = null;
       script.onerror = e => error = e;
       document.head.appendChild(script);
+      // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
       if (error) {
         throw error;
       }
@@ -1864,6 +1868,7 @@ export class Frame extends SdkObject {
       }
 
       // Clean Service Workers
+      // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
       const registrations = navigator.serviceWorker ? await navigator.serviceWorker.getRegistrations() : [];
       await Promise.all(registrations.map(async r => {
         // Heuristic for service workers that stalled during main script fetch or importScripts:
@@ -1879,6 +1884,7 @@ export class Frame extends SdkObject {
       }));
 
       // Clean IndexedDB
+      // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
       for (const db of await indexedDB.databases() || []) {
         // Do not wait for the callback - it is called on timer in Chromium (slow).
         if (db.name) {
diff --git a/packages/playwright-core/src/server/injected/ariaSnapshot.ts b/packages/playwright-core/src/server/injected/ariaSnapshot.ts
index 69a9ffb0b7..20300fb87c 100644
--- a/packages/playwright-core/src/server/injected/ariaSnapshot.ts
+++ b/packages/playwright-core/src/server/injected/ariaSnapshot.ts
@@ -202,6 +202,7 @@ function normalizeStringChildren(rootA11yNode: AriaNode) {
   const visit = (ariaNode: AriaNode) => {
     const normalizedChildren: (AriaNode | string)[] = [];
     const buffer: string[] = [];
+    // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
     for (const child of ariaNode.children || []) {
       if (typeof child === 'string') {
         buffer.push(child);
@@ -296,6 +297,7 @@ function matchesNode(node: AriaNode | string, template: AriaTemplateNode, depth:
     if (!matchesName(node.name, template)) {
       return false;
     }
+    // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
     if (!containsList(node.children || [], template.children || [], depth)) {
       return false;
     }
@@ -335,6 +337,7 @@ function matchesNodeDeep(root: AriaNode, template: AriaTemplateNode, collectAll:
     if (typeof node === 'string') {
       return false;
     }
+    // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
     for (const child of node.children || []) {
       if (visit(child)) {
         return true;
@@ -414,6 +417,7 @@ export function renderAriaTree(ariaNode: AriaNode, options?: { mode?: 'raw' | 'r
       }
     } else {
       lines.push(escapedKey + ':');
+      // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
       for (const child of ariaNode.children || []) {
         visit(child, ariaNode, indent + '  ');
       }
@@ -422,6 +426,7 @@ export function renderAriaTree(ariaNode: AriaNode, options?: { mode?: 'raw' | 'r
 
   if (ariaNode.role === 'fragment') {
     // Render fragment.
+    // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
     for (const child of ariaNode.children || []) {
       visit(child, ariaNode, '');
     }
diff --git a/packages/playwright-core/src/server/injected/clock.ts b/packages/playwright-core/src/server/injected/clock.ts
index 576591bb9c..a3b132ec1c 100644
--- a/packages/playwright-core/src/server/injected/clock.ts
+++ b/packages/playwright-core/src/server/injected/clock.ts
@@ -157,6 +157,7 @@ export class ClockController {
     }
 
     let firstException: Error | undefined;
+    // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
     while (true) {
       const result = await this._callFirstTimer(to);
       if (!result.timerFound) {
@@ -428,6 +429,7 @@ export class ClockController {
         isPaused = false;
       } else if (type === 'setFixedTime') {
         this._innerSetFixedTime(asWallTime(param!));
+        // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
       } else if (type === 'setSystemTime') {
         this._innerSetTime(asWallTime(param!));
       }
diff --git a/packages/playwright-core/src/server/injected/domUtils.ts b/packages/playwright-core/src/server/injected/domUtils.ts
index 397021b8cf..5c7c3ac3e2 100644
--- a/packages/playwright-core/src/server/injected/domUtils.ts
+++ b/packages/playwright-core/src/server/injected/domUtils.ts
@@ -43,6 +43,7 @@ export function parentElementOrShadowHost(element: Element): Element | undefined
   if (!element.parentNode) {
     return;
   }
+  // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
   if (element.parentNode.nodeType === 11 /* Node.DOCUMENT_FRAGMENT_NODE */ && (element.parentNode as ShadowRoot).host) {
     return (element.parentNode as ShadowRoot).host;
   }
@@ -80,6 +81,7 @@ export function closestCrossShadow(element: Element | undefined, css: string, sc
 }
 
 export function getElementComputedStyle(element: Element, pseudo?: string): CSSStyleDeclaration | undefined {
+  // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
   return element.ownerDocument && element.ownerDocument.defaultView ? element.ownerDocument.defaultView.getComputedStyle(element, pseudo) : undefined;
 }
 
@@ -94,6 +96,7 @@ export function isElementStyleVisibilityVisible(element: Element, style?: CSSSty
   // All the browser implement it, but WebKit has a bug which prevents us from using it:
   // https://bugs.webkit.org/show_bug.cgi?id=264733
   // @ts-ignore
+  // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
   if (Element.prototype.checkVisibility && browserNameForWorkarounds !== 'webkit') {
     if (!element.checkVisibility()) {
       return false;
diff --git a/packages/playwright-core/src/server/injected/highlight.ts b/packages/playwright-core/src/server/injected/highlight.ts
index 69b4bcad27..790a086368 100644
--- a/packages/playwright-core/src/server/injected/highlight.ts
+++ b/packages/playwright-core/src/server/injected/highlight.ts
@@ -92,6 +92,7 @@ export class Highlight {
 
   install() {
     // NOTE: document.documentElement can be null: https://github.com/microsoft/TypeScript/issues/50078
+    // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
     if (this._injectedScript.document.documentElement && !this._injectedScript.document.documentElement.contains(this._glassPaneElement)) {
       this._injectedScript.document.documentElement.appendChild(this._glassPaneElement);
     }
diff --git a/packages/playwright-core/src/server/injected/injectedScript.ts b/packages/playwright-core/src/server/injected/injectedScript.ts
index 0c8f8aed2f..ebb0d5559f 100644
--- a/packages/playwright-core/src/server/injected/injectedScript.ts
+++ b/packages/playwright-core/src/server/injected/injectedScript.ts
@@ -271,11 +271,6 @@ export class InjectedScript {
       throw this.createStacklessError('Node is not queryable.');
     }
 
-    if (selector.capture !== undefined) {
-      // We should have handled the capture above.
-      throw this.createStacklessError('Internal error: there should not be a capture in the selector.');
-    }
-
     // Workaround so that ":scope" matches the ShadowRoot.
     // This is, unfortunately, because an ElementHandle can point to any Node (including ShadowRoot/Document/etc),
     // and not just to an Element, and we support various APIs on ElementHandle like "textContent()".
@@ -531,6 +526,7 @@ export class InjectedScript {
   }
 
   describeIFrameStyle(iframe: Element): 'error:notconnected' | 'transformed' | { left: number, top: number } {
+    // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
     if (!iframe.ownerDocument || !iframe.ownerDocument.defaultView) {
       return 'error:notconnected';
     }
@@ -687,6 +683,7 @@ export class InjectedScript {
       return !disabled && !readonly;
     }
 
+    // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
     if (state === 'checked' || state === 'unchecked') {
       const need = state === 'checked';
       const checked = getChecked(element, false);
@@ -718,6 +715,7 @@ export class InjectedScript {
         }
         let matches = true;
         if (optionToSelect.valueOrLabel !== undefined) {
+          // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
           matches = matches && (optionToSelect.valueOrLabel === option.value || optionToSelect.valueOrLabel === option.label);
         }
         if (optionToSelect.value !== undefined) {
@@ -835,6 +833,7 @@ export class InjectedScript {
     }
 
     const { activeElement, isFocused: wasFocused } = this._activelyFocused(node);
+    // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
     if ((node as HTMLElement).isContentEditable && !wasFocused && activeElement && (activeElement as HTMLElement | SVGElement).blur) {
       // Workaround the Firefox bug where focusing the element does not switch current
       // contenteditable to the new element. However, blurring the previous one helps.
@@ -899,7 +898,7 @@ export class InjectedScript {
 
     // Get all component roots leading to the target element.
     // Go from the bottom to the top to make it work with closed shadow roots.
-    let parentElement = targetElement;
+    let parentElement = targetElement as Element | undefined;
     while (parentElement) {
       const root = enclosingShadowRootOrDocument(parentElement);
       if (!root) {
@@ -1054,10 +1053,12 @@ export class InjectedScript {
       }
 
       // Determine the event point. Note that Firefox does not always have window.TouchEvent.
+      // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
       const point = (!!this.window.TouchEvent && (event instanceof this.window.TouchEvent)) ? event.touches[0] : (event as MouseEvent | PointerEvent);
 
       // Check that we hit the right element at the first event, and assume all
       // subsequent events will be fine.
+      // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
       if (result === undefined && point) {
         result = this.expectHitTarget({ x: point.clientX, y: point.clientY }, element);
       }
@@ -1265,6 +1266,8 @@ export class InjectedScript {
       // New documentElement - let's check whether listeners are still here.
       seenEvent = false;
       this.window.dispatchEvent(new CustomEvent(customEventName));
+      // TODO: Dead code?
+      // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
       if (seenEvent) {
         return;
       }
diff --git a/packages/playwright-core/src/server/injected/roleUtils.ts b/packages/playwright-core/src/server/injected/roleUtils.ts
index 611bbcefee..ed75c7e9f0 100644
--- a/packages/playwright-core/src/server/injected/roleUtils.ts
+++ b/packages/playwright-core/src/server/injected/roleUtils.ts
@@ -128,12 +128,13 @@ const kImplicitRoleByTagName: { [tagName: string]: (e: Element) => AriaRole | nu
     }
     if (['email', 'tel', 'text', 'url', ''].includes(type)) {
       // https://html.spec.whatwg.org/multipage/input.html#concept-input-list
-      const list = getIdRefs(e, e.getAttribute('list'))[0];
+      const list = getIdRefs(e, e.getAttribute('list'))[0] as Element | undefined;
       return (list && elementSafeTagName(list) === 'DATALIST') ? 'combobox' : 'textbox';
     }
     if (type === 'hidden') {
       return null;
     }
+    // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
     return inputTypeToRole[type] || 'textbox';
   },
   'INS': () => 'insertion',
@@ -206,10 +207,11 @@ function getImplicitAriaRole(element: Element): AriaRole | null {
   }
   // Inherit presentation role when required.
   // https://www.w3.org/TR/wai-aria-1.2/#conflict_resolution_presentation_none
-  let ancestor: Element | null = element;
+  let ancestor = element as Element | null;
   while (ancestor) {
     const parent = parentElementOrShadowHost(ancestor);
     const parents = kPresentationInheritanceParents[elementSafeTagName(ancestor)];
+    // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
     if (!parents || !parent || !parents.includes(elementSafeTagName(parent))) {
       break;
     }
@@ -233,7 +235,7 @@ const validRoles: AriaRole[] = ['alert', 'alertdialog', 'application', 'article'
 function getExplicitAriaRole(element: Element): AriaRole | null {
   // https://www.w3.org/TR/wai-aria-1.2/#document-handling_author-errors_roles
   const roles = (element.getAttribute('role') || '').split(' ').map(role => role.trim());
-  return roles.find(role => validRoles.includes(role as any)) as AriaRole || null;
+  return (roles.find(role => validRoles.includes(role as any)) as AriaRole | undefined) || null;
 }
 
 function hasPresentationConflictResolution(element: Element, role: string | null) {
@@ -661,6 +663,7 @@ function getTextAlternativeInternal(element: Element, options: AccessibleNameOpt
     // https://w3c.github.io/html-aam/#button-element-accessible-name-computation
     if (!labelledBy && tagName === 'BUTTON') {
       options.visitedElements.add(element);
+      // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
       const labels = (element as HTMLButtonElement).labels || [];
       if (labels.length) {
         return getAccessibleNameFromAssociatedLabels(labels, options);
@@ -671,6 +674,7 @@ function getTextAlternativeInternal(element: Element, options: AccessibleNameOpt
     // https://w3c.github.io/html-aam/#output-element-accessible-name-computation
     if (!labelledBy && tagName === 'OUTPUT') {
       options.visitedElements.add(element);
+      // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
       const labels = (element as HTMLOutputElement).labels || [];
       if (labels.length) {
         return getAccessibleNameFromAssociatedLabels(labels, options);
diff --git a/packages/playwright-core/src/server/injected/selectorEvaluator.ts b/packages/playwright-core/src/server/injected/selectorEvaluator.ts
index 30dfa264ae..c41928254f 100644
--- a/packages/playwright-core/src/server/injected/selectorEvaluator.ts
+++ b/packages/playwright-core/src/server/injected/selectorEvaluator.ts
@@ -20,6 +20,7 @@ import { isElementVisible, parentElementOrShadowHost } from './domUtils';
 import { type LayoutSelectorName, layoutSelectorScore } from './layoutSelectorUtils';
 import { elementMatchesText, elementText, shouldSkipForTextMatching, type ElementText } from './selectorUtils';
 import { normalizeWhiteSpace } from '../../utils/isomorphic/stringUtils';
+import { assertUnreachableWithError } from 'playwright-core/lib/common/types';
 
 type QueryContext = {
   scope: Element | Document;
@@ -280,66 +281,70 @@ export class SelectorEvaluatorImpl implements SelectorEvaluator {
     }
     return this._cached<boolean>(this._cacheMatchesParents, element, [complex, index, context.scope, context.pierceShadow, context.originalScope], () => {
       const { selector: simple, combinator } = complex.simples[index];
-      if (combinator === '>') {
-        const parent = parentElementOrShadowHostInContext(element, context);
-        if (!parent || !this._matchesSimple(parent, simple, context)) {
+      switch (combinator) {
+        case '>': {
+          const parent = parentElementOrShadowHostInContext(element, context);
+          if (!parent || !this._matchesSimple(parent, simple, context)) {
+            return false;
+          }
+          return this._matchesParents(parent, complex, index - 1, context);
+        }
+        case '+': {
+          const previousSibling = previousSiblingInContext(element, context);
+          if (!previousSibling || !this._matchesSimple(previousSibling, simple, context)) {
+            return false;
+          }
+          return this._matchesParents(previousSibling, complex, index - 1, context);
+        }
+        case '': {
+          let parent = parentElementOrShadowHostInContext(element, context);
+          while (parent) {
+            if (this._matchesSimple(parent, simple, context)) {
+              if (this._matchesParents(parent, complex, index - 1, context)) {
+                return true;
+              }
+              if (complex.simples[index - 1].combinator === '') {
+                break;
+              }
+            }
+            parent = parentElementOrShadowHostInContext(parent, context);
+          }
           return false;
         }
-        return this._matchesParents(parent, complex, index - 1, context);
-      }
-      if (combinator === '+') {
-        const previousSibling = previousSiblingInContext(element, context);
-        if (!previousSibling || !this._matchesSimple(previousSibling, simple, context)) {
+        case '~': {
+          let previousSibling = previousSiblingInContext(element, context);
+          while (previousSibling) {
+            if (this._matchesSimple(previousSibling, simple, context)) {
+              if (this._matchesParents(previousSibling, complex, index - 1, context)) {
+                return true;
+              }
+              if (complex.simples[index - 1].combinator === '~') {
+                break;
+              }
+            }
+            previousSibling = previousSiblingInContext(previousSibling, context);
+          }
           return false;
         }
-        return this._matchesParents(previousSibling, complex, index - 1, context);
-      }
-      if (combinator === '') {
-        let parent = parentElementOrShadowHostInContext(element, context);
-        while (parent) {
-          if (this._matchesSimple(parent, simple, context)) {
-            if (this._matchesParents(parent, complex, index - 1, context)) {
-              return true;
-            }
-            if (complex.simples[index - 1].combinator === '') {
-              break;
+        case '>=': {
+          let parent: Element | undefined = element;
+          while (parent) {
+            if (this._matchesSimple(parent, simple, context)) {
+              if (this._matchesParents(parent, complex, index - 1, context)) {
+                return true;
+              }
+              if (complex.simples[index - 1].combinator === '') {
+                break;
+              }
             }
+            parent = parentElementOrShadowHostInContext(parent, context);
           }
-          parent = parentElementOrShadowHostInContext(parent, context);
+          return false;
         }
-        return false;
-      }
-      if (combinator === '~') {
-        let previousSibling = previousSiblingInContext(element, context);
-        while (previousSibling) {
-          if (this._matchesSimple(previousSibling, simple, context)) {
-            if (this._matchesParents(previousSibling, complex, index - 1, context)) {
-              return true;
-            }
-            if (complex.simples[index - 1].combinator === '~') {
-              break;
-            }
-          }
-          previousSibling = previousSiblingInContext(previousSibling, context);
+        default: {
+          return assertUnreachableWithError(combinator, new Error(`Unsupported combinator "${combinator}"`));
         }
-        return false;
       }
-      if (combinator === '>=') {
-        let parent: Element | undefined = element;
-        while (parent) {
-          if (this._matchesSimple(parent, simple, context)) {
-            if (this._matchesParents(parent, complex, index - 1, context)) {
-              return true;
-            }
-            if (complex.simples[index - 1].combinator === '') {
-              break;
-            }
-          }
-          parent = parentElementOrShadowHostInContext(parent, context);
-        }
-        return false;
-      }
-      throw new Error(`Unsupported combinator "${combinator}"`);
     });
   }
 
@@ -461,6 +466,7 @@ const scopeEngine: SelectorEngine = {
     const actualScope = context.originalScope || context.scope;
     if (actualScope.nodeType === 9 /* Node.DOCUMENT_NODE */) {
       const root = (actualScope as Document).documentElement;
+      // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
       return root ? [root] : [];
     }
     if (actualScope.nodeType === 1 /* Node.ELEMENT_NODE */) {
diff --git a/packages/playwright-core/src/server/injected/selectorGenerator.ts b/packages/playwright-core/src/server/injected/selectorGenerator.ts
index d581336f61..68983cb9ad 100644
--- a/packages/playwright-core/src/server/injected/selectorGenerator.ts
+++ b/packages/playwright-core/src/server/injected/selectorGenerator.ts
@@ -193,7 +193,7 @@ function generateSelectorFor(injectedScript: InjectedScript, targetElement: Elem
       // This is best theoretically possible candidate from the current parent.
       // We use the fact that widening the scope to grand-parent makes any selector
       // even less likely to match.
-      let bestPossibleInParent: SelectorToken[] | null = candidates[0];
+      let bestPossibleInParent = candidates[0] as SelectorToken[] | null;
       if (!bestPossibleInParent) {
         return;
       }
@@ -442,7 +442,7 @@ function cssFallback(injectedScript: InjectedScript, targetElement: Element, opt
       bestTokenForLevel = token;
     }
 
-    const parent = element.parentNode as (Element | ShadowRoot);
+    const parent = element.parentNode as (Element | ShadowRoot | null);
 
     // Combine class names until unique.
     const classes = [...element.classList];
diff --git a/packages/playwright-core/src/server/injected/selectorUtils.ts b/packages/playwright-core/src/server/injected/selectorUtils.ts
index ce5b900466..12f02eaeb2 100644
--- a/packages/playwright-core/src/server/injected/selectorUtils.ts
+++ b/packages/playwright-core/src/server/injected/selectorUtils.ts
@@ -55,6 +55,7 @@ export function matchesAttributePart(value: any, attr: AttributeSelectorPart) {
   if (attr.op === '|=') {
     return objValue === attrValue || objValue.startsWith(attrValue + '-');
   }
+  // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
   if (attr.op === '~=') {
     return objValue.split(' ').includes(attrValue);
   }
@@ -63,6 +64,7 @@ export function matchesAttributePart(value: any, attr: AttributeSelectorPart) {
 
 export function shouldSkipForTextMatching(element: Element | ShadowRoot) {
   const document = element.ownerDocument;
+  // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
   return element.nodeName === 'SCRIPT' || element.nodeName === 'NOSCRIPT' || element.nodeName === 'STYLE' || document.head && document.head.contains(element);
 }
 
diff --git a/packages/playwright-core/src/server/injected/xpathSelectorEngine.ts b/packages/playwright-core/src/server/injected/xpathSelectorEngine.ts
index ff705335e1..48d33dce0c 100644
--- a/packages/playwright-core/src/server/injected/xpathSelectorEngine.ts
+++ b/packages/playwright-core/src/server/injected/xpathSelectorEngine.ts
@@ -23,6 +23,7 @@ export const XPathEngine: SelectorEngine = {
     }
     const result: Element[] = [];
     const document = root.ownerDocument || root;
+    // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
     if (!document) {
       return result;
     }
diff --git a/packages/playwright-core/src/server/isomorphic/utilityScriptSerializers.ts b/packages/playwright-core/src/server/isomorphic/utilityScriptSerializers.ts
index 5c1c5d5d4b..9ec461769b 100644
--- a/packages/playwright-core/src/server/isomorphic/utilityScriptSerializers.ts
+++ b/packages/playwright-core/src/server/isomorphic/utilityScriptSerializers.ts
@@ -72,6 +72,7 @@ export function source() {
     if (Object.is(value, undefined)) {
       return undefined;
     }
+    // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
     if (typeof value === 'object' && value) {
       if ('ref' in value) {
         return refs.get(value.ref);
@@ -92,6 +93,7 @@ export function source() {
         if (value.v === '-Infinity') {
           return -Infinity;
         }
+        // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
         if (value.v === '-0') {
           return -0;
         }
diff --git a/packages/playwright-core/src/server/launchApp.ts b/packages/playwright-core/src/server/launchApp.ts
index 55f63f4cf4..b1c49ba7cd 100644
--- a/packages/playwright-core/src/server/launchApp.ts
+++ b/packages/playwright-core/src/server/launchApp.ts
@@ -90,6 +90,7 @@ export async function syncLocalStorageWithSettings(page: Page, appName: string)
   await page.addInitScript(
       `(${String((settings: any) => {
         // iframes w/ snapshots, etc.
+        // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
         if (location && location.protocol === 'data:') {
           return;
         }
diff --git a/packages/playwright-core/src/server/page.ts b/packages/playwright-core/src/server/page.ts
index 4ceded9999..26d21ffa76 100644
--- a/packages/playwright-core/src/server/page.ts
+++ b/packages/playwright-core/src/server/page.ts
@@ -494,6 +494,7 @@ export class Page extends SdkObject {
       return;
     }
     const mainFrame = this._frameManager.mainFrame();
+    // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
     if (!mainFrame || !mainFrame.pendingDocument()) {
       return;
     }
@@ -619,11 +620,11 @@ export class Page extends SdkObject {
   async expectScreenshot(metadata: CallMetadata, options: ExpectScreenshotOptions = {}): Promise<{ actual?: Buffer, previous?: Buffer, diff?: Buffer, errorMessage?: string, log?: string[] }> {
     const locator = options.locator;
     const rafrafScreenshot = locator ? async (progress: Progress, timeout: number) => {
-      return await locator.frame.rafrafTimeoutScreenshotElementWithProgress(progress, locator.selector, timeout, options || {});
+      return await locator.frame.rafrafTimeoutScreenshotElementWithProgress(progress, locator.selector, timeout, options);
     } : async (progress: Progress, timeout: number) => {
       await this.performActionPreChecks(progress);
       await this.mainFrame().rafrafTimeout(timeout);
-      return await this._screenshotter.screenshotPage(progress, options || {});
+      return await this._screenshotter.screenshotPage(progress, options);
     };
 
     const comparator = getComparator('image/png');
@@ -632,7 +633,7 @@ export class Page extends SdkObject {
       return { errorMessage: '"not" matcher requires expected result' };
     }
     try {
-      const format = validateScreenshotOptions(options || {});
+      const format = validateScreenshotOptions(options);
       if (format !== 'png') {
         throw new Error('Only PNG screenshots are supported');
       }
@@ -667,6 +668,7 @@ export class Page extends SdkObject {
         progress.log(`  generating new stable screenshot expectation`);
       }
       let isFirstIteration = true;
+      // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
       while (true) {
         progress.throwIfAborted();
         if (this.isClosed()) {
diff --git a/packages/playwright-core/src/server/recorder.ts b/packages/playwright-core/src/server/recorder.ts
index 5e846b3595..aad553eaff 100644
--- a/packages/playwright-core/src/server/recorder.ts
+++ b/packages/playwright-core/src/server/recorder.ts
@@ -63,7 +63,7 @@ export class Recorder implements InstrumentationListener, IRecorder {
   }
 
   static show(codegenMode: 'actions' | 'trace-events', context: BrowserContext, recorderAppFactory: IRecorderAppFactory, params: channels.BrowserContextEnableRecorderParams): Promise<Recorder> {
-    let recorderPromise = (context as any)[recorderSymbol] as Promise<Recorder>;
+    let recorderPromise = (context as any)[recorderSymbol] as Promise<Recorder> | undefined;
     if (!recorderPromise) {
       recorderPromise = Recorder._create(codegenMode, context, recorderAppFactory, params);
       (context as any)[recorderSymbol] = recorderPromise;
@@ -135,6 +135,7 @@ export class Recorder implements InstrumentationListener, IRecorder {
         this._contextRecorder.clearScript();
         return;
       }
+      // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
       if (data.event === 'runTask') {
         this._contextRecorder.runTask(data.params.task);
         return;
diff --git a/packages/playwright-core/src/server/recorder/chat.ts b/packages/playwright-core/src/server/recorder/chat.ts
index 5d36506ed4..5bbcfc231e 100644
--- a/packages/playwright-core/src/server/recorder/chat.ts
+++ b/packages/playwright-core/src/server/recorder/chat.ts
@@ -105,6 +105,7 @@ function iterablePump(): ChunkIterator {
 
   const iterable = (async function* () {
     const reader = stream.getReader();
+    // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
     while (true) {
       const { done, value } = await reader.read();
       if (done) {
diff --git a/packages/playwright-core/src/server/recorder/contextRecorder.ts b/packages/playwright-core/src/server/recorder/contextRecorder.ts
index 26c71f2f64..f9fc6181d7 100644
--- a/packages/playwright-core/src/server/recorder/contextRecorder.ts
+++ b/packages/playwright-core/src/server/recorder/contextRecorder.ts
@@ -283,13 +283,14 @@ export class ContextRecorder extends EventEmitter {
 
 export async function generateFrameSelector(frame: Frame): Promise<string[]> {
   const selectorPromises: Promise<string>[] = [];
-  while (frame) {
-    const parent = frame.parentFrame();
+  let currentFrame = frame as Frame | undefined;
+  while (currentFrame) {
+    const parent = currentFrame.parentFrame();
     if (!parent) {
       break;
     }
-    selectorPromises.push(generateFrameSelectorInParent(parent, frame));
-    frame = parent;
+    selectorPromises.push(generateFrameSelectorInParent(parent, currentFrame));
+    currentFrame = parent;
   }
   const result = await Promise.all(selectorPromises);
   return result.reverse();
@@ -299,6 +300,7 @@ async function generateFrameSelectorInParent(parent: Frame, frame: Frame): Promi
   const result = await raceAgainstDeadline(async () => {
     try {
       const frameElement = await frame.frameElement();
+      // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
       if (!frameElement || !parent) {
         return;
       }
diff --git a/packages/playwright-core/src/server/recorder/recorderCollection.ts b/packages/playwright-core/src/server/recorder/recorderCollection.ts
index 4c5a1b2009..714537c957 100644
--- a/packages/playwright-core/src/server/recorder/recorderCollection.ts
+++ b/packages/playwright-core/src/server/recorder/recorderCollection.ts
@@ -91,7 +91,7 @@ export class RecorderCollection extends EventEmitter {
 
     if (signal.name === 'navigation' && frame._page.mainFrame() === frame) {
       const timestamp = monotonicTime();
-      const lastAction = this._actions[this._actions.length - 1];
+      const lastAction = this._actions[this._actions.length - 1] as actions.ActionInContext | undefined;
       const signalThreshold = isUnderTest() ? 500 : 5000;
 
       let generateGoto = false;
diff --git a/packages/playwright-core/src/server/recorder/recorderUtils.ts b/packages/playwright-core/src/server/recorder/recorderUtils.ts
index 4ba5bac30a..a8c28eb64e 100644
--- a/packages/playwright-core/src/server/recorder/recorderUtils.ts
+++ b/packages/playwright-core/src/server/recorder/recorderUtils.ts
@@ -98,7 +98,7 @@ export function callMetadataForAction(pageAliases: Map<Page, string>, actionInCo
 export function collapseActions(actions: actions.ActionInContext[]): actions.ActionInContext[] {
   const result: actions.ActionInContext[] = [];
   for (const action of actions) {
-    const lastAction = result[result.length - 1];
+    const lastAction = result[result.length - 1] as actions.ActionInContext | undefined;
     const isSameAction = lastAction && lastAction.action.name === action.action.name && lastAction.frame.pageAlias === action.frame.pageAlias && lastAction.frame.framePath.join('|') === action.frame.framePath.join('|');
     const isSameSelector = lastAction && 'selector' in lastAction.action && 'selector' in action.action && action.action.selector === lastAction.action.selector;
     const shouldMerge = isSameAction && (action.action.name === 'navigate' || (action.action.name === 'fill' && isSameSelector));
diff --git a/packages/playwright-core/src/server/registry/browserFetcher.ts b/packages/playwright-core/src/server/registry/browserFetcher.ts
index a302c2927d..ea0604f2b9 100644
--- a/packages/playwright-core/src/server/registry/browserFetcher.ts
+++ b/packages/playwright-core/src/server/registry/browserFetcher.ts
@@ -138,7 +138,7 @@ function getDownloadProgress(): OnProgressCallback {
 }
 
 function getAnimatedDownloadProgress(): OnProgressCallback {
-  let progressBar: ProgressBar;
+  let progressBar: ProgressBar | undefined;
   let lastDownloadedBytes = 0;
 
   return (downloadedBytes: number, totalBytes: number) => {
diff --git a/packages/playwright-core/src/server/screenshotter.ts b/packages/playwright-core/src/server/screenshotter.ts
index 925aa5b31c..3e31d0065e 100644
--- a/packages/playwright-core/src/server/screenshotter.ts
+++ b/packages/playwright-core/src/server/screenshotter.ts
@@ -188,6 +188,7 @@ export class Screenshotter {
 
   private async _fullPageSize(progress: Progress): Promise<types.Size> {
     const fullPageSize = await this._page.mainFrame().waitForFunctionValueInUtility(progress, () => {
+      // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
       if (!document.body || !document.documentElement) {
         return null;
       }
@@ -297,6 +298,7 @@ export class Screenshotter {
       return cleanup;
     }
 
+    // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
     await Promise.all((options.mask || []).map(async ({ frame, selector }) => {
       const pair = await frame.selectors.resolveFrameForSelector(selector);
       if (pair) {
@@ -378,6 +380,7 @@ export function validateScreenshotOptions(options: ScreenshotOptions): 'png' | '
   // options.type takes precedence over inferring the type from options.path
   // because it may be a 0-length file with no extension created beforehand (i.e. as a temp file).
   if (options.type) {
+    // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
     assert(options.type === 'png' || options.type === 'jpeg', 'Unknown options.type value: ' + options.type);
     format = options.type;
   }
diff --git a/packages/playwright-core/src/server/selectors.ts b/packages/playwright-core/src/server/selectors.ts
index 309f250d28..dd89c440cd 100644
--- a/packages/playwright-core/src/server/selectors.ts
+++ b/packages/playwright-core/src/server/selectors.ts
@@ -91,6 +91,7 @@ export class Selectors {
     });
     return {
       parsed,
+      // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
       world: needsMainWorld ? 'main' as const : 'utility' as const,
       strict,
     };
diff --git a/packages/playwright-core/src/server/trace/recorder/snapshotter.ts b/packages/playwright-core/src/server/trace/recorder/snapshotter.ts
index b819510c75..948aee5398 100644
--- a/packages/playwright-core/src/server/trace/recorder/snapshotter.ts
+++ b/packages/playwright-core/src/server/trace/recorder/snapshotter.ts
@@ -113,7 +113,7 @@ export class Snapshotter {
 
     // In each frame, in a non-stalling manner, capture the snapshots.
     const snapshots = page.frames().map(async frame => {
-      const data = await frame.nonStallingRawEvaluateInExistingMainContext(expression).catch(e => debugLogger.log('error', e)) as SnapshotData;
+      const data = await frame.nonStallingRawEvaluateInExistingMainContext(expression).catch(e => debugLogger.log('error', e)) as SnapshotData | undefined;
       // Something went wrong -> bail out, our snapshots are best-efforty.
       if (!data || !this._started) {
         return;
diff --git a/packages/playwright-core/src/server/trace/recorder/snapshotterInjected.ts b/packages/playwright-core/src/server/trace/recorder/snapshotterInjected.ts
index ad74db9b5a..e6da2c882a 100644
--- a/packages/playwright-core/src/server/trace/recorder/snapshotterInjected.ts
+++ b/packages/playwright-core/src/server/trace/recorder/snapshotterInjected.ts
@@ -133,6 +133,7 @@ export function frameSnapshotStreamer(snapshotStreamer: string, removeNoScript:
           // New documentElement - let's check whether listeners are still here.
           seenEvent = false;
           window.dispatchEvent(new CustomEvent(customEventName));
+          // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
           if (!seenEvent) {
             // Listener did not fire. Reattach the listener and notify.
             window.addEventListener(customEventName, handleCustomEvent);
@@ -163,7 +164,7 @@ export function frameSnapshotStreamer(snapshotStreamer: string, removeNoScript:
     }
 
     private _interceptNativeMethod(obj: any, method: string, cb: (thisObj: any, result: any) => void) {
-      const native = obj[method] as Function;
+      const native = obj[method] as Function | undefined;
       if (!native) {
         return;
       }
@@ -175,7 +176,7 @@ export function frameSnapshotStreamer(snapshotStreamer: string, removeNoScript:
     }
 
     private _interceptNativeAsyncMethod(obj: any, method: string, cb: (thisObj: any, result: any) => void) {
-      const native = obj[method] as Function;
+      const native = obj[method] as Function | undefined;
       if (!native) {
         return;
       }
@@ -436,11 +437,9 @@ export function frameSnapshotStreamer(snapshotStreamer: string, removeNoScript:
 
         const visitChildStyleSheet = (child: CSSStyleSheet) => {
           const snapshot = visitStyleSheet(child);
-          if (snapshot) {
-            result.push(snapshot.n);
-            expectValue(child);
-            equals = equals && snapshot.equals;
-          }
+          result.push(snapshot.n);
+          expectValue(child);
+          equals = equals && snapshot.equals;
         };
 
         if (nodeType === Node.DOCUMENT_FRAGMENT_NODE) {
@@ -482,6 +481,7 @@ export function frameSnapshotStreamer(snapshotStreamer: string, removeNoScript:
             expectValue(value);
             attrs[kBoundingRectAttribute] = value;
           }
+          // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
           if ((element as HTMLElement).popover && (element as HTMLElement).matches && (element as HTMLElement).matches(':popover-open')) {
             const value = 'true';
             expectValue(kPopoverOpenAttribute);
@@ -626,6 +626,7 @@ export function frameSnapshotStreamer(snapshotStreamer: string, removeNoScript:
       };
 
       let html: NodeSnapshot;
+      // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
       if (document.documentElement) {
         const { n } = visitNode(document.documentElement)!;
         html = n;
diff --git a/packages/playwright-core/src/server/trace/recorder/tracing.ts b/packages/playwright-core/src/server/trace/recorder/tracing.ts
index aef7d867a3..d53bd96f81 100644
--- a/packages/playwright-core/src/server/trace/recorder/tracing.ts
+++ b/packages/playwright-core/src/server/trace/recorder/tracing.ts
@@ -405,9 +405,7 @@ export class Tracing extends SdkObject implements InstrumentationListener, Snaps
     const error = await this._fs.syncAndGetError();
 
     this._isStopping = false;
-    if (this._state) {
-      this._state.recording = false;
-    }
+    this._state.recording = false;
 
     // IMPORTANT: no awaits after this point, to make sure recording state is correct.
 
diff --git a/packages/playwright-core/src/server/transport.ts b/packages/playwright-core/src/server/transport.ts
index abb5363b91..68e1eef455 100644
--- a/packages/playwright-core/src/server/transport.ts
+++ b/packages/playwright-core/src/server/transport.ts
@@ -118,6 +118,7 @@ export class WebSocketTransport implements ConnectionTransport {
 
     if (result.redirect) {
       // Strip authorization headers from the redirected request.
+      // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
       const newHeaders = Object.fromEntries(Object.entries(headers || {}).filter(([name]) => {
         return !name.includes('access-key') && name.toLowerCase() !== 'authorization';
       }));
diff --git a/packages/playwright-core/src/server/webkit/wkBrowser.ts b/packages/playwright-core/src/server/webkit/wkBrowser.ts
index b5bf747e2c..d78389cf7b 100644
--- a/packages/playwright-core/src/server/webkit/wkBrowser.ts
+++ b/packages/playwright-core/src/server/webkit/wkBrowser.ts
@@ -164,7 +164,7 @@ export class WKBrowser extends Browser {
       context = this._contexts.get(event.browserContextId) || null;
     }
     if (!context) {
-      context = this._defaultContext as WKBrowserContext;
+      context = this._defaultContext as WKBrowserContext | null;
     }
     if (!context) {
       return;
diff --git a/packages/playwright-core/src/server/webkit/wkPage.ts b/packages/playwright-core/src/server/webkit/wkPage.ts
index 5056971db3..108452a4fa 100644
--- a/packages/playwright-core/src/server/webkit/wkPage.ts
+++ b/packages/playwright-core/src/server/webkit/wkPage.ts
@@ -198,6 +198,7 @@ export class WKPage implements PageDelegate {
       promises.push(this.updateUserAgent());
     }
     const emulatedMedia = this._page.emulatedMedia();
+    // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
     if (emulatedMedia.media || emulatedMedia.colorScheme || emulatedMedia.reducedMotion || emulatedMedia.forcedColors) {
       promises.push(WKPage._setEmulateMedia(session, emulatedMedia.media, emulatedMedia.colorScheme, emulatedMedia.reducedMotion, emulatedMedia.forcedColors));
     }
@@ -274,6 +275,7 @@ export class WKPage implements PageDelegate {
     this._pageProxySession.dispose();
     eventsHelper.removeEventListeners(this._sessionListeners);
     eventsHelper.removeEventListeners(this._eventListeners);
+    // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
     if (this._session) {
       this._session.dispose();
     }
@@ -1038,6 +1040,7 @@ export class WKPage implements PageDelegate {
       frameId: frame._id,
       executionContextId: ((context as any)[contextDelegateSymbol] as WKExecutionContext)._contextId
     });
+    // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
     if (!result || result.object.subtype === 'null') {
       throw new Error('Frame has been detached.');
     }
diff --git a/packages/playwright-core/src/server/webkit/wkWorkers.ts b/packages/playwright-core/src/server/webkit/wkWorkers.ts
index f587d2c5a1..bd968d0845 100644
--- a/packages/playwright-core/src/server/webkit/wkWorkers.ts
+++ b/packages/playwright-core/src/server/webkit/wkWorkers.ts
@@ -60,14 +60,14 @@ export class WKWorkers {
         });
       }),
       eventsHelper.addEventListener(session, 'Worker.dispatchMessageFromWorker', (event: Protocol.Worker.dispatchMessageFromWorkerPayload) => {
-        const workerSession = this._workerSessions.get(event.workerId)!;
+        const workerSession = this._workerSessions.get(event.workerId);
         if (!workerSession) {
           return;
         }
         workerSession.dispatchMessage(JSON.parse(event.message));
       }),
       eventsHelper.addEventListener(session, 'Worker.workerTerminated', (event: Protocol.Worker.workerTerminatedPayload) => {
-        const workerSession = this._workerSessions.get(event.workerId)!;
+        const workerSession = this._workerSessions.get(event.workerId);
         if (!workerSession) {
           return;
         }
diff --git a/packages/playwright-core/src/utils/comparators.ts b/packages/playwright-core/src/utils/comparators.ts
index 8521071806..60574d051a 100644
--- a/packages/playwright-core/src/utils/comparators.ts
+++ b/packages/playwright-core/src/utils/comparators.ts
@@ -45,6 +45,7 @@ export function compareBuffersOrStrings(actualBuffer: Buffer | string, expectedB
   if (typeof actualBuffer === 'string') {
     return compareText(actualBuffer, expectedBuffer);
   }
+  // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
   if (!actualBuffer || !(actualBuffer instanceof Buffer)) {
     return { errorMessage: 'Actual result should be a Buffer or a string.' };
   }
diff --git a/packages/playwright-core/src/utils/headers.ts b/packages/playwright-core/src/utils/headers.ts
index 6c0370fea9..2169ceffe7 100644
--- a/packages/playwright-core/src/utils/headers.ts
+++ b/packages/playwright-core/src/utils/headers.ts
@@ -23,7 +23,7 @@ export function headersObjectToArray(headers: HeadersObject, separator?: string,
   }
   const result: HeadersArray = [];
   for (const name in headers) {
-    const values = headers[name];
+    const values = headers[name] as string | undefined;
     if (values === undefined) {
       continue;
     }
diff --git a/packages/playwright-core/src/utils/isomorphic/ariaSnapshot.ts b/packages/playwright-core/src/utils/isomorphic/ariaSnapshot.ts
index c2af9845ef..7880eb85d2 100644
--- a/packages/playwright-core/src/utils/isomorphic/ariaSnapshot.ts
+++ b/packages/playwright-core/src/utils/isomorphic/ariaSnapshot.ts
@@ -230,6 +230,7 @@ class KeyParser {
 
   private _readAttributes(result: AriaTemplateRoleNode) {
     let errorPos = this._pos;
+    // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
     while (true) {
       this._skipWhitespace();
       if (this._peek() === '[') {
diff --git a/packages/playwright-core/src/utils/isomorphic/cssParser.ts b/packages/playwright-core/src/utils/isomorphic/cssParser.ts
index c4dc750afe..4d2f4b5abf 100644
--- a/packages/playwright-core/src/utils/isomorphic/cssParser.ts
+++ b/packages/playwright-core/src/utils/isomorphic/cssParser.ts
@@ -132,6 +132,7 @@ export function parseCSS(selector: string, customNames: Set<string>): { selector
 
   function consumeFunctionArguments(): CSSFunctionArgument[] {
     const result = [consumeArgument()];
+    // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
     while (true) {
       skipWhitespace();
       if (!isComma()) {
@@ -163,6 +164,7 @@ export function parseCSS(selector: string, customNames: Set<string>): { selector
     } else {
       result.simples.push({ selector: consumeSimpleSelector(), combinator: '' });
     }
+    // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
     while (true) {
       skipWhitespace();
       if (isClauseCombinator()) {
diff --git a/packages/playwright-core/src/utils/isomorphic/cssTokenizer.ts b/packages/playwright-core/src/utils/isomorphic/cssTokenizer.ts
index 72b21e1898..2e460621d0 100644
--- a/packages/playwright-core/src/utils/isomorphic/cssTokenizer.ts
+++ b/packages/playwright-core/src/utils/isomorphic/cssTokenizer.ts
@@ -317,6 +317,7 @@ export function tokenize(str1: string): CSSTokenInterface[] {
   const consumeComments = function() {
     while (next(1) === 0x2f && next(2) === 0x2a) {
       consume(2);
+      // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
       while (true) {
         consume();
         if (code === 0x2a && next() === 0x2f) {
diff --git a/packages/playwright-core/src/utils/isomorphic/locatorGenerators.ts b/packages/playwright-core/src/utils/isomorphic/locatorGenerators.ts
index ee62d70b89..aa6eef41d3 100644
--- a/packages/playwright-core/src/utils/isomorphic/locatorGenerators.ts
+++ b/packages/playwright-core/src/utils/isomorphic/locatorGenerators.ts
@@ -16,7 +16,7 @@
 
 import { escapeWithQuotes, normalizeEscapedRegexQuotes, toSnakeCase, toTitleCase } from './stringUtils';
 import { type NestedSelectorBody, parseAttributeSelector, parseSelector, stringifySelector } from './selectorParser';
-import type { ParsedSelector } from './selectorParser';
+import type { ParsedSelector, ParsedSelectorPart } from './selectorParser';
 
 export type Language = 'javascript' | 'python' | 'java' | 'csharp' | 'jsonl';
 export type LocatorType = 'default' | 'role' | 'text' | 'label' | 'placeholder' | 'alt' | 'title' | 'test-id' | 'nth' | 'first' | 'last' | 'has-text' | 'has-not-text' | 'has' | 'hasNot' | 'frame' | 'frame-locator' | 'and' | 'or' | 'chain';
@@ -177,7 +177,7 @@ function innerAsLocators(factory: LocatorFactory, parsed: ParsedSelector, isFram
       continue;
     }
 
-    const nextPart = parts[index + 1];
+    const nextPart = parts[index + 1] as ParsedSelectorPart | undefined;
 
     const selectorPart = stringifySelector({ parts: [part] });
     const locatorPart = factory.generateLocator(base, 'default', selectorPart);
diff --git a/packages/playwright-core/src/utils/isomorphic/locatorParser.ts b/packages/playwright-core/src/utils/isomorphic/locatorParser.ts
index 904cf88b5a..dffa943f02 100644
--- a/packages/playwright-core/src/utils/isomorphic/locatorParser.ts
+++ b/packages/playwright-core/src/utils/isomorphic/locatorParser.ts
@@ -111,6 +111,7 @@ function shiftParams(template: string, sub: number) {
 function transform(template: string, params: TemplateParams, testIdAttributeName: string): string {
   // Recursively handle filter(has=, hasnot=, sethas(), sethasnot()).
   // TODO: handle and(locator), or(locator), locator(locator), locator(has=, hasnot=, sethas(), sethasnot()).
+  // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
   while (true) {
     const hasMatch = template.match(/filter\(,?(has=|hasnot=|sethas\(|sethasnot\()/);
     if (!hasMatch) {
diff --git a/packages/playwright-core/src/utils/isomorphic/selectorParser.ts b/packages/playwright-core/src/utils/isomorphic/selectorParser.ts
index 8da49aaad7..31b04d0aa2 100644
--- a/packages/playwright-core/src/utils/isomorphic/selectorParser.ts
+++ b/packages/playwright-core/src/utils/isomorphic/selectorParser.ts
@@ -328,6 +328,7 @@ export function parseAttributeSelector(selector: string, allowUnquotedStrings: b
     while (!EOL) {
       if (next() === '\\') {
         source += eat1();
+        // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
         if (EOL) {
           syntaxError('parsing regular expression');
         }
diff --git a/packages/playwright-core/src/utils/isomorphic/urlMatch.ts b/packages/playwright-core/src/utils/isomorphic/urlMatch.ts
index 386a55bc85..7abb311d54 100644
--- a/packages/playwright-core/src/utils/isomorphic/urlMatch.ts
+++ b/packages/playwright-core/src/utils/isomorphic/urlMatch.ts
@@ -30,13 +30,13 @@ export function globToRegex(glob: string): RegExp {
       continue;
     }
     if (c === '*') {
-      const beforeDeep = glob[i - 1];
+      const beforeDeep = glob[i - 1] as string | undefined;
       let starCount = 1;
       while (glob[i + 1] === '*') {
         starCount++;
         i++;
       }
-      const afterDeep = glob[i + 1];
+      const afterDeep = glob[i + 1] as string | undefined;
       const isDeep = starCount > 1 &&
           (beforeDeep === '/' || beforeDeep === undefined) &&
           (afterDeep === '/' || afterDeep === undefined);
diff --git a/packages/playwright-core/src/utils/network.ts b/packages/playwright-core/src/utils/network.ts
index 5e9a933643..c40cf349fa 100644
--- a/packages/playwright-core/src/utils/network.ts
+++ b/packages/playwright-core/src/utils/network.ts
@@ -80,17 +80,15 @@ export function httpRequest(params: HTTPRequestParams, onResponse: (r: http.Inco
     https.request(options, requestCallback) :
     http.request(options, requestCallback);
   request.on('error', onError);
-  if (timeout !== undefined) {
-    const rejectOnTimeout = () =>  {
-      onError(new Error(`Request to ${params.url} timed out after ${timeout}ms`));
-      request.abort();
-    };
-    if (timeout <= 0) {
-      rejectOnTimeout();
-      return;
-    }
-    request.setTimeout(timeout, rejectOnTimeout);
+  const rejectOnTimeout = () =>  {
+    onError(new Error(`Request to ${params.url} timed out after ${timeout}ms`));
+    request.abort();
+  };
+  if (timeout <= 0) {
+    rejectOnTimeout();
+    return;
   }
+  request.setTimeout(timeout, rejectOnTimeout);
   request.end(params.data);
 }
 
diff --git a/packages/playwright-core/src/utils/timeoutRunner.ts b/packages/playwright-core/src/utils/timeoutRunner.ts
index c44ce0ffff..8752d256db 100644
--- a/packages/playwright-core/src/utils/timeoutRunner.ts
+++ b/packages/playwright-core/src/utils/timeoutRunner.ts
@@ -36,6 +36,7 @@ export async function pollAgainstDeadline<T>(callback: () => Promise<{ continueP
   const lastPollInterval = pollIntervals.pop() ?? 1000;
   let lastResult: T|undefined;
   const wrappedCallback = () => Promise.resolve().then(callback);
+  // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
   while (true) {
     const time = monotonicTime();
     if (deadline && time >= deadline) {
diff --git a/packages/playwright-core/src/utils/zipFile.ts b/packages/playwright-core/src/utils/zipFile.ts
index d9c95398bf..bcea3da753 100644
--- a/packages/playwright-core/src/utils/zipFile.ts
+++ b/packages/playwright-core/src/utils/zipFile.ts
@@ -51,13 +51,14 @@ export class ZipFile {
 
   async read(entryPath: string): Promise<Buffer> {
     await this._openedPromise;
-    const entry = this._entries.get(entryPath)!;
+    const entry = this._entries.get(entryPath);
     if (!entry) {
       throw new Error(`${entryPath} not found in file ${this._fileName}`);
     }
 
     return new Promise((resolve, reject) => {
       this._zipFile!.openReadStream(entry, (error, readStream) => {
+        // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
         if (error || !readStream) {
           reject(error || 'Entry not found');
           return;
diff --git a/packages/playwright-ct-core/src/vitePlugin.ts b/packages/playwright-ct-core/src/vitePlugin.ts
index b339b826ec..7df627e737 100644
--- a/packages/playwright-ct-core/src/vitePlugin.ts
+++ b/packages/playwright-ct-core/src/vitePlugin.ts
@@ -254,6 +254,7 @@ function vitePlugin(registerSource: string, templateDir: string, buildInfo: Buil
     async transform(this: PluginContext, content, id) {
       const queryIndex = id.indexOf('?');
       const file = queryIndex !== -1 ? id.substring(0, queryIndex) : id;
+      // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
       if (!buildInfo.sources[file]) {
         try {
           const timestamp = (await fs.promises.stat(file)).mtimeMs;
diff --git a/packages/playwright-ct-react/registerSource.mjs b/packages/playwright-ct-react/registerSource.mjs
index a3572e6978..49df35c138 100644
--- a/packages/playwright-ct-react/registerSource.mjs
+++ b/packages/playwright-ct-react/registerSource.mjs
@@ -52,6 +52,7 @@ function __pwRender(value) {
       if (isJsxFragment(type)) {
         type = __pwReact.Fragment;
       }
+      // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
       const props = component.props ? __pwRender(component.props) : {};
       const key = component.key ? __pwRender(component.key) : undefined;
       const { children, ...propsWithoutChildren } = props;
diff --git a/packages/playwright-ct-react17/registerSource.mjs b/packages/playwright-ct-react17/registerSource.mjs
index 12fbe189a3..3e19b87842 100644
--- a/packages/playwright-ct-react17/registerSource.mjs
+++ b/packages/playwright-ct-react17/registerSource.mjs
@@ -39,6 +39,7 @@ function __pwRender(value) {
   return window.__pwTransformObject(value, v => {
     if (isJsxComponent(v)) {
       const component = v;
+      // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
       const props = component.props ? __pwRender(component.props) : {};
       const key = component.key ? __pwRender(component.key) : undefined;
       const { children, ...propsWithoutChildren } = props;
diff --git a/packages/playwright-ct-svelte/registerSource.mjs b/packages/playwright-ct-svelte/registerSource.mjs
index 06a324a197..2ed6ce99ae 100644
--- a/packages/playwright-ct-svelte/registerSource.mjs
+++ b/packages/playwright-ct-svelte/registerSource.mjs
@@ -112,6 +112,7 @@ window.playwrightMount = async (component, rootElement, hooksConfig) => {
 
 window.playwrightUnmount = async rootElement => {
   const svelteComponent = /** @type {SvelteComponent} */ (rootElement[__pwSvelteComponentKey]);
+  // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
   if (!svelteComponent) {
     throw new Error('Component was not mounted');
   }
@@ -125,6 +126,7 @@ window.playwrightUpdate = async (rootElement, component) => {
   }
 
   const svelteComponent = /** @type {SvelteComponent} */ (rootElement[__pwSvelteComponentKey]);
+  // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
   if (!svelteComponent) {
     throw new Error('Component was not mounted');
   }
diff --git a/packages/playwright/bundles/expect/third_party/asymmetricMatchers.ts b/packages/playwright/bundles/expect/third_party/asymmetricMatchers.ts
index 6767e28ccb..23149203e6 100644
--- a/packages/playwright/bundles/expect/third_party/asymmetricMatchers.ts
+++ b/packages/playwright/bundles/expect/third_party/asymmetricMatchers.ts
@@ -42,6 +42,7 @@ const utils = Object.freeze({
 });
 
 function getPrototype(obj: object) {
+  // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
   if (Object.getPrototypeOf) {
     return Object.getPrototypeOf(obj);
   }
diff --git a/packages/playwright/bundles/expect/third_party/index.ts b/packages/playwright/bundles/expect/third_party/index.ts
index 7328c7eb5c..fd52f4d494 100644
--- a/packages/playwright/bundles/expect/third_party/index.ts
+++ b/packages/playwright/bundles/expect/third_party/index.ts
@@ -323,6 +323,7 @@ const makeThrowingMatcher = (
 
           // Try to remove this function from the stack trace frame.
           // Guard for some environments (browsers) that do not support this feature.
+          // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
           if (Error.captureStackTrace) {
             Error.captureStackTrace(error, throwingMatcher);
           }
@@ -350,6 +351,7 @@ const makeThrowingMatcher = (
         !(error instanceof JestAssertionError) &&
         error.name !== 'PrettyFormatPluginError' &&
         // Guard for some environments (browsers) that do not support this feature.
+        // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
         Error.captureStackTrace
       ) {
         // Try to remove this and deeper functions from the stack trace frame.
@@ -373,6 +375,7 @@ const makeThrowingMatcher = (
 
       if (isPromise(potentialResult)) {
         const asyncError = new JestAssertionError();
+        // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
         if (Error.captureStackTrace) {
           Error.captureStackTrace(asyncError, throwingMatcher);
         }
@@ -432,6 +435,7 @@ const _validateResult = (result: any) => {
 
 function assertions(expected: number): void {
   const error = new Error();
+  // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
   if (Error.captureStackTrace) {
     Error.captureStackTrace(error, assertions);
   }
@@ -444,6 +448,7 @@ function assertions(expected: number): void {
 }
 function hasAssertions(...args: Array<unknown>): void {
   const error = new Error();
+  // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
   if (Error.captureStackTrace) {
     Error.captureStackTrace(error, hasAssertions);
   }
diff --git a/packages/playwright/src/common/configLoader.ts b/packages/playwright/src/common/configLoader.ts
index 4b650e941d..d4c484732f 100644
--- a/packages/playwright/src/common/configLoader.ts
+++ b/packages/playwright/src/common/configLoader.ts
@@ -133,6 +133,7 @@ export async function loadConfig(location: ConfigLocation, overrides?: ConfigCLI
 }
 
 function validateConfig(file: string, config: Config) {
+  // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
   if (typeof config !== 'object' || !config) {
     throw errorWithFile(file, `Configuration file must export a single object`);
   }
@@ -239,7 +240,7 @@ function validateConfig(file: string, config: Config) {
   }
 
   if ('reportSlowTests' in config && config.reportSlowTests !== undefined && config.reportSlowTests !== null) {
-    if (!config.reportSlowTests || typeof config.reportSlowTests !== 'object') {
+    if (typeof config.reportSlowTests !== 'object') {
       throw errorWithFile(file, `config.reportSlowTests must be an object`);
     }
     if (!('max' in config.reportSlowTests) || typeof config.reportSlowTests.max !== 'number' || config.reportSlowTests.max < 0) {
@@ -251,7 +252,7 @@ function validateConfig(file: string, config: Config) {
   }
 
   if ('shard' in config && config.shard !== undefined && config.shard !== null) {
-    if (!config.shard || typeof config.shard !== 'object') {
+    if (typeof config.shard !== 'object') {
       throw errorWithFile(file, `config.shard must be an object`);
     }
     if (!('total' in config.shard) || typeof config.shard.total !== 'number' || config.shard.total < 1) {
@@ -278,6 +279,7 @@ function validateConfig(file: string, config: Config) {
 }
 
 function validateProject(file: string, project: Project, title: string) {
+  // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
   if (typeof project !== 'object' || !project) {
     throw errorWithFile(file, `${title} must be an object`);
   }
@@ -334,7 +336,7 @@ function validateProject(file: string, project: Project, title: string) {
   }
 
   if ('use' in project && project.use !== undefined) {
-    if (!project.use || typeof project.use !== 'object') {
+    if (typeof project.use !== 'object') {
       throw errorWithFile(file, `${title}.use must be an object`);
     }
   }
diff --git a/packages/playwright/src/common/fixtures.ts b/packages/playwright/src/common/fixtures.ts
index c631ee55e4..b9a74c86d6 100644
--- a/packages/playwright/src/common/fixtures.ts
+++ b/packages/playwright/src/common/fixtures.ts
@@ -213,6 +213,7 @@ export class FixturePool {
     }
 
     // If no errors found, iterate over boxed fixtures
+    // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
     if (!hasDependencyErrors) {
       for (const name of names) {
         const registration = this._registrations.get(name)!;
@@ -260,6 +261,7 @@ export class FixturePool {
 const signatureSymbol = Symbol('signature');
 
 export function formatPotentiallyInternalLocation(location: Location): string {
+  // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
   const isUserFixture = location && filterStackFile(location.file);
   return isUserFixture ? formatLocation(location) : '<builtin>';
 }
@@ -317,6 +319,7 @@ function filterOutComments(s: string): string {
       if (s[i - 1] === '*' && s[i] === '/') {
         commentState = 'none';
       }
+      // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
     } else if (commentState === 'none') {
       if (s[i] === '/' && s[i + 1] === '/') {
         commentState = 'singleline';
diff --git a/packages/playwright/src/common/test.ts b/packages/playwright/src/common/test.ts
index c5bbdfdc24..5a34980584 100644
--- a/packages/playwright/src/common/test.ts
+++ b/packages/playwright/src/common/test.ts
@@ -285,6 +285,7 @@ export class TestCase extends Base implements reporterTypes.TestCase {
   }
 
   titlePath(): string[] {
+    // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
     const titlePath = this.parent ? this.parent.titlePath() : [];
     titlePath.push(this.title);
     return titlePath;
diff --git a/packages/playwright/src/common/testType.ts b/packages/playwright/src/common/testType.ts
index bb9288fb47..5fecdb2258 100644
--- a/packages/playwright/src/common/testType.ts
+++ b/packages/playwright/src/common/testType.ts
@@ -337,7 +337,7 @@ export const rootTestType = new TestTypeImpl([]);
 export function mergeTests(...tests: TestType<any, any>[]) {
   let result = rootTestType;
   for (const t of tests) {
-    const testTypeImpl = (t as any)[testTypeSymbol] as TestTypeImpl;
+    const testTypeImpl = (t as any)[testTypeSymbol] as TestTypeImpl | undefined;
     if (!testTypeImpl) {
       throw new Error(`mergeTests() accepts "test" functions as parameters.\nDid you mean to call test.extend() with fixtures instead?`);
     }
diff --git a/packages/playwright/src/index.ts b/packages/playwright/src/index.ts
index ec44f6f7de..e503374537 100644
--- a/packages/playwright/src/index.ts
+++ b/packages/playwright/src/index.ts
@@ -77,6 +77,7 @@ const playwrightFixtures: Fixtures<TestFixtures, WorkerFixtures> = ({
       handleSIGINT: false,
       ...launchOptions,
     };
+    // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
     if (headless !== undefined) {
       options.headless = headless;
     }
@@ -179,6 +180,7 @@ const playwrightFixtures: Fixtures<TestFixtures, WorkerFixtures> = ({
     serviceWorkers,
   }, use) => {
     const options: BrowserContextOptions = {};
+    /* eslint-disable @typescript-eslint/no-unnecessary-condition */
     if (acceptDownloads !== undefined) {
       options.acceptDownloads = acceptDownloads;
     }
@@ -245,6 +247,7 @@ const playwrightFixtures: Fixtures<TestFixtures, WorkerFixtures> = ({
     if (serviceWorkers !== undefined) {
       options.serviceWorkers = serviceWorkers;
     }
+    /* eslint-enable @typescript-eslint/no-unnecessary-condition */
     await use({
       ...contextOptions,
       ...options,
@@ -454,7 +457,7 @@ const playwrightFixtures: Fixtures<TestFixtures, WorkerFixtures> = ({
     }
 
     // First time we are reusing the context, we should create the page.
-    let [page] = context.pages();
+    let page = context.pages()[0] as Page | undefined;
     if (!page) {
       page = await context.newPage();
     }
diff --git a/packages/playwright/src/isomorphic/teleReceiver.ts b/packages/playwright/src/isomorphic/teleReceiver.ts
index c6026cd494..84e855eb04 100644
--- a/packages/playwright/src/isomorphic/teleReceiver.ts
+++ b/packages/playwright/src/isomorphic/teleReceiver.ts
@@ -494,6 +494,7 @@ export class TeleTestCase implements reporterTypes.TestCase {
   }
 
   titlePath(): string[] {
+    // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
     const titlePath = this.parent ? this.parent.titlePath() : [];
     titlePath.push(this.title);
     return titlePath;
diff --git a/packages/playwright/src/isomorphic/testTree.ts b/packages/playwright/src/isomorphic/testTree.ts
index 0763f36967..071121277c 100644
--- a/packages/playwright/src/isomorphic/testTree.ts
+++ b/packages/playwright/src/isomorphic/testTree.ts
@@ -106,7 +106,7 @@ export class TestTree {
 
       for (const test of parentSuite.tests) {
         const title = test.title;
-        let testCaseItem = parentGroup.children.find(t => t.kind !== 'group' && t.title === title) as TestCaseItem;
+        let testCaseItem = parentGroup.children.find(t => t.kind !== 'group' && t.title === title) as TestCaseItem | undefined;
         if (!testCaseItem) {
           testCaseItem = {
             kind: 'case',
@@ -135,9 +135,9 @@ export class TestTree {
           status = 'skipped';
         } else if (result.status === 'interrupted') {
           status = 'none';
-        } else if (result && test.outcome() !== 'expected') {
+        } else if (test.outcome() !== 'expected') {
           status = 'failed';
-        } else if (result && test.outcome() === 'expected') {
+        } else if (test.outcome() === 'expected') {
           status = 'passed';
         }
 
diff --git a/packages/playwright/src/matchers/toMatchAriaSnapshot.ts b/packages/playwright/src/matchers/toMatchAriaSnapshot.ts
index 408e9ee44f..a000d558e3 100644
--- a/packages/playwright/src/matchers/toMatchAriaSnapshot.ts
+++ b/packages/playwright/src/matchers/toMatchAriaSnapshot.ts
@@ -66,7 +66,7 @@ export async function toMatchAriaSnapshot(
     } else if (expectedParam.name) {
       expectedPath = testInfo.snapshotPath(sanitizeFilePathBeforeExtension(expectedParam.name));
     } else {
-      let snapshotNames = (testInfo as any)[snapshotNamesSymbol] as SnapshotNames;
+      let snapshotNames = (testInfo as any)[snapshotNamesSymbol] as SnapshotNames | undefined;
       if (!snapshotNames) {
         snapshotNames = { anonymousSnapshotIndex: 0 };
         (testInfo as any)[snapshotNamesSymbol] = snapshotNames;
@@ -107,6 +107,7 @@ export async function toMatchAriaSnapshot(
   const receivedText = typedReceived.raw;
   const message = () => {
     if (pass) {
+      // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
       if (notFound) {
         return messagePrefix + `Expected: not ${this.utils.printExpected(expected)}\nReceived: ${receivedText}` + callLogText(log);
       }
@@ -114,6 +115,7 @@ export async function toMatchAriaSnapshot(
       return messagePrefix + `Expected: not ${this.utils.printExpected(expected)}\nReceived: ${printedReceived}` + callLogText(log);
     } else {
       const labelExpected = `Expected`;
+      // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
       if (notFound) {
         return messagePrefix + `${labelExpected}: ${this.utils.printExpected(expected)}\nReceived: ${receivedText}` + callLogText(log);
       }
diff --git a/packages/playwright/src/matchers/toMatchSnapshot.ts b/packages/playwright/src/matchers/toMatchSnapshot.ts
index d5b746bbf2..57d1520d90 100644
--- a/packages/playwright/src/matchers/toMatchSnapshot.ts
+++ b/packages/playwright/src/matchers/toMatchSnapshot.ts
@@ -198,6 +198,7 @@ class SnapshotHelper {
       message: () => message,
       log,
     };
+    // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
     return Object.fromEntries(Object.entries(unfiltered).filter(([_, v]) => v !== undefined)) as ImageMatcherResult;
   }
 
diff --git a/packages/playwright/src/matchers/toMatchText.ts b/packages/playwright/src/matchers/toMatchText.ts
index 2f8bc34b21..3789ebda57 100644
--- a/packages/playwright/src/matchers/toMatchText.ts
+++ b/packages/playwright/src/matchers/toMatchText.ts
@@ -45,6 +45,7 @@ export async function toMatchText(
 
   if (
     !(typeof expected === 'string') &&
+    // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
     !(expected && typeof expected.test === 'function')
   ) {
     // Same format as jest's matcherErrorMessage
diff --git a/packages/playwright/src/plugins/gitCommitInfoPlugin.ts b/packages/playwright/src/plugins/gitCommitInfoPlugin.ts
index f30c0b2a7c..3322644d64 100644
--- a/packages/playwright/src/plugins/gitCommitInfoPlugin.ts
+++ b/packages/playwright/src/plugins/gitCommitInfoPlugin.ts
@@ -36,6 +36,7 @@ export const gitCommitInfo = (options?: GitCommitInfoPluginOptions): TestRunnerP
         info['revision.timestamp'] = timestamp.getTime();
       }
 
+      // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
       config.metadata = config.metadata || {};
       Object.assign(config.metadata, info);
     },
diff --git a/packages/playwright/src/reporters/json.ts b/packages/playwright/src/reporters/json.ts
index 8e5cd87068..fd924791dc 100644
--- a/packages/playwright/src/reporters/json.ts
+++ b/packages/playwright/src/reporters/json.ts
@@ -157,6 +157,7 @@ class JSONReporter implements ReporterV2 {
       }
     }
 
+    // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
     for (const spec of from.specs || []) {
       const toSpec = to.specs.find(s => s.title === spec.title && s.file === toPosixPath(path.relative(this.config.rootDir, spec.file)) && s.line === spec.line && s.column === spec.column);
       if (toSpec) {
diff --git a/packages/playwright/src/reporters/merge.ts b/packages/playwright/src/reporters/merge.ts
index d0cee62fba..d71da31a45 100644
--- a/packages/playwright/src/reporters/merge.ts
+++ b/packages/playwright/src/reporters/merge.ts
@@ -363,6 +363,7 @@ class UniqueFileNameGenerator {
     const extension = path.extname(name);
     name = name.substring(0, name.length - extension.length);
     let index = 0;
+    // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
     while (true) {
       const candidate = `${name}-${++index}${extension}`;
       if (!this._usedNames.has(candidate)) {
@@ -412,6 +413,7 @@ class IdsPatcher {
   }
 
   private _onProject(project: JsonProject) {
+    // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
     project.metadata ??= {};
     project.suites.forEach(suite => this._updateTestIds(suite));
   }
diff --git a/packages/playwright/src/reporters/reporterV2.ts b/packages/playwright/src/reporters/reporterV2.ts
index 60cb63a96a..3fadbeb774 100644
--- a/packages/playwright/src/reporters/reporterV2.ts
+++ b/packages/playwright/src/reporters/reporterV2.ts
@@ -40,6 +40,7 @@ type StdIOChunk = {
 
 export function wrapReporterAsV2(reporter: Reporter | ReporterV2): ReporterV2 {
   try {
+    // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
     if ('version' in reporter && reporter.version() === 'v2') {
       return reporter as ReporterV2;
     }
diff --git a/packages/playwright/src/runner/dispatcher.ts b/packages/playwright/src/runner/dispatcher.ts
index 98e43fc055..b1993787a4 100644
--- a/packages/playwright/src/runner/dispatcher.ts
+++ b/packages/playwright/src/runner/dispatcher.ts
@@ -375,7 +375,7 @@ class JobDispatcher {
   }
 
   private _onAttach(params: AttachmentPayload) {
-    const data = this._dataByTestId.get(params.testId)!;
+    const data = this._dataByTestId.get(params.testId);
     if (!data) {
       // The test has finished, but attachments are still coming. Just ignore them.
       return;
diff --git a/packages/playwright/src/runner/lastRun.ts b/packages/playwright/src/runner/lastRun.ts
index f48542b3f8..50ea122f89 100644
--- a/packages/playwright/src/runner/lastRun.ts
+++ b/packages/playwright/src/runner/lastRun.ts
@@ -18,7 +18,7 @@ import fs from 'fs';
 import path from 'path';
 import type { FullResult, Suite } from '../../types/testReporter';
 import { filterProjects } from './projectUtils';
-import type { FullConfigInternal } from '../common/config';
+import type { FullConfigInternal, FullProjectInternal } from '../common/config';
 import type { ReporterV2 } from '../reporters/reporterV2';
 
 type LastRunInfo = {
@@ -33,7 +33,7 @@ export class LastRunReporter implements ReporterV2 {
 
   constructor(config: FullConfigInternal) {
     this._config = config;
-    const [project] = filterProjects(config.projects, config.cliProjectFilter);
+    const project = filterProjects(config.projects, config.cliProjectFilter)[0] as FullProjectInternal | undefined;
     if (project) {
       this._lastRunFile = path.join(project.project.outputDir, '.last-run.json');
     }
diff --git a/packages/playwright/src/runner/rebase.ts b/packages/playwright/src/runner/rebase.ts
index 097b9f4db1..50da4e98e0 100644
--- a/packages/playwright/src/runner/rebase.ts
+++ b/packages/playwright/src/runner/rebase.ts
@@ -20,7 +20,7 @@ import type { T } from '../transform/babelBundle';
 import { types, traverse, babelParse } from '../transform/babelBundle';
 import { MultiMap } from 'playwright-core/lib/utils';
 import { colors, diff } from 'playwright-core/lib/utilsBundle';
-import type { FullConfigInternal } from '../common/config';
+import type { FullConfigInternal, FullProjectInternal } from '../common/config';
 import { filterProjects } from './projectUtils';
 import type { InternalReporter } from '../reporters/internalReporter';
 const t: typeof T = types;
@@ -50,7 +50,7 @@ export async function applySuggestedRebaselines(config: FullConfigInternal, repo
   if (!suggestedRebaselines.size) {
     return;
   }
-  const [project] = filterProjects(config.projects, config.cliProjectFilter);
+  const project = filterProjects(config.projects, config.cliProjectFilter)[0] as FullProjectInternal | undefined;
   if (!project) {
     return;
   }
@@ -197,6 +197,7 @@ function applyPatchWithConflictMarkers(oldText: string, newText: string) {
     }
   });
 
+  // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
   if (conflict) {
     result += '>>>>>>> SNAPSHOT\n';
   }
diff --git a/packages/playwright/src/runner/tasks.ts b/packages/playwright/src/runner/tasks.ts
index 405f7a5c91..8ab8acb078 100644
--- a/packages/playwright/src/runner/tasks.ts
+++ b/packages/playwright/src/runner/tasks.ts
@@ -216,6 +216,7 @@ function createRemoveOutputDirsTask(): Task<TestRun> {
       projects.forEach(p => outputDirs.add(p.project.outputDir));
 
       await Promise.all(Array.from(outputDirs).map(outputDir => removeFolders([outputDir]).then(async ([error]) => {
+        // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
         if (!error) {
           return;
         }
diff --git a/packages/playwright/src/runner/testServer.ts b/packages/playwright/src/runner/testServer.ts
index d56f1dece1..1dcf3a4be4 100644
--- a/packages/playwright/src/runner/testServer.ts
+++ b/packages/playwright/src/runner/testServer.ts
@@ -423,6 +423,7 @@ export class TestServerDispatcher implements TestServerInterface {
       // Preserve plugin instances between setup and build.
       if (!this._plugins) {
         webServerPluginsForConfig(config).forEach(p => config.plugins.push({ factory: p }));
+        // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
         this._plugins = config.plugins || [];
       } else {
         config.plugins.splice(0, config.plugins.length, ...this._plugins);
diff --git a/packages/playwright/src/runner/watchMode.ts b/packages/playwright/src/runner/watchMode.ts
index bb3172554f..3c4ac01f60 100644
--- a/packages/playwright/src/runner/watchMode.ts
+++ b/packages/playwright/src/runner/watchMode.ts
@@ -140,6 +140,7 @@ export async function runWatchModeLoop(configLocation: ConfigLocation, initialOp
   let lastRun: { type: 'changed' | 'regular' | 'failed', failedTestIds?: string[], dirtyTestIds?: string[] } = { type: 'regular' };
   let result: FullResult['status'] = 'passed';
 
+  // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
   while (true) {
     if (bufferMode) {
       printBufferPrompt(dirtyTestFiles, teleSuiteUpdater.config!.rootDir);
@@ -244,9 +245,9 @@ export async function runWatchModeLoop(configLocation: ConfigLocation, initialOp
     if (command === 'repeat') {
       if (lastRun.type === 'regular') {
         await runTests(options, testServerConnection, { title: 're-running tests' });
-        continue;
       } else if (lastRun.type === 'changed') {
         await runTests(options, testServerConnection, { title: 're-running tests', testIds: lastRun.dirtyTestIds });
+      // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
       } else if (lastRun.type === 'failed') {
         await runTests({}, testServerConnection, { title: 're-running tests', testIds: lastRun.failedTestIds });
       }
diff --git a/packages/playwright/src/transform/transform.ts b/packages/playwright/src/transform/transform.ts
index 3c602abcbd..93b125c80b 100644
--- a/packages/playwright/src/transform/transform.ts
+++ b/packages/playwright/src/transform/transform.ts
@@ -96,6 +96,7 @@ function loadAndValidateTsconfigsForFolder(folder: string): ParsedTsConfigData[]
   const foldersWithConfig: string[] = [];
   let currentFolder = path.resolve(folder);
   let result: ParsedTsConfigData[] | undefined;
+  // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
   while (true) {
     const cached = cachedTSConfigs.get(currentFolder);
     if (cached) {
@@ -299,6 +300,7 @@ function installTransformIfNeeded() {
 
   const originalResolveFilename = (Module as any)._resolveFilename;
   function resolveFilename(this: any, specifier: string, parent: Module, ...rest: any[]) {
+    // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
     if (parent) {
       const resolved = resolveHook(parent.filename, specifier);
       if (resolved !== undefined) {
diff --git a/packages/playwright/src/worker/fixtureRunner.ts b/packages/playwright/src/worker/fixtureRunner.ts
index 1789d573af..6bcb8c04fe 100644
--- a/packages/playwright/src/worker/fixtureRunner.ts
+++ b/packages/playwright/src/worker/fixtureRunner.ts
@@ -41,6 +41,7 @@ class Fixture {
     this.registration = registration;
     this.value = null;
     const shouldGenerateStep = !this.registration.box && !this.registration.option;
+    // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
     const isUserFixture = this.registration.location && filterStackFile(this.registration.location.file);
     const title = this.registration.customTitle || this.registration.name;
     const location = isUserFixture ? this.registration.location : undefined;
diff --git a/packages/playwright/src/worker/testInfo.ts b/packages/playwright/src/worker/testInfo.ts
index 0c6740034a..5139605563 100644
--- a/packages/playwright/src/worker/testInfo.ts
+++ b/packages/playwright/src/worker/testInfo.ts
@@ -228,6 +228,7 @@ export class TestInfoImpl implements TestInfo {
     } else if (type === 'skip' || type === 'fixme') {
       this.expectedStatus = 'skipped';
       throw new SkipError('Test is skipped: ' + (description || ''));
+    // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
     } else if (type === 'fail') {
       if (this.expectedStatus !== 'skipped') {
         this.expectedStatus = 'failed';
@@ -330,6 +331,7 @@ export class TestInfoImpl implements TestInfo {
       location: data.location,
     };
     this._onStepBegin(payload);
+    // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
     this._tracing.appendBeforeActionForStep(stepId, parentStep?.stepId, data.apiName || data.title, data.params, data.location ? [data.location] : []);
     return step;
   }
diff --git a/packages/playwright/src/worker/testTracing.ts b/packages/playwright/src/worker/testTracing.ts
index ccd7a5c181..0ae8dcb099 100644
--- a/packages/playwright/src/worker/testTracing.ts
+++ b/packages/playwright/src/worker/testTracing.ts
@@ -98,6 +98,7 @@ export class TestTracing {
     } else if (typeof value === 'string') {
       this._options = { ...defaultTraceOptions, mode: value === 'retry-with-trace' ? 'on-first-retry' : value as TraceMode };
     } else {
+      // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
       const mode = value.mode || 'off';
       this._options = { ...defaultTraceOptions, ...value, mode: (mode as string) === 'retry-with-trace' ? 'on-first-retry' : mode };
     }
@@ -235,7 +236,7 @@ export class TestTracing {
 
   appendForError(error: TestInfoErrorImpl) {
     const rawStack = error.stack?.split('\n') || [];
-    const stack = rawStack ? filteredStackTrace(rawStack) : [];
+    const stack = filteredStackTrace(rawStack);
     this._appendTraceEvent({
       type: 'error',
       message: this._formatError(error),
diff --git a/packages/playwright/src/worker/timeoutManager.ts b/packages/playwright/src/worker/timeoutManager.ts
index 1b6776e34f..916030ed86 100644
--- a/packages/playwright/src/worker/timeoutManager.ts
+++ b/packages/playwright/src/worker/timeoutManager.ts
@@ -99,6 +99,7 @@ export class TimeoutManager {
         running.timeoutPromise,
       ]);
     } finally {
+      // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
       if (running.timer) {
         clearTimeout(running.timer);
       }
diff --git a/packages/playwright/src/worker/workerMain.ts b/packages/playwright/src/worker/workerMain.ts
index 270e55a187..1e48cb21a8 100644
--- a/packages/playwright/src/worker/workerMain.ts
+++ b/packages/playwright/src/worker/workerMain.ts
@@ -187,6 +187,7 @@ export class WorkerMain extends ProcessRunner {
   }
 
   private async _loadIfNeeded() {
+    // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
     if (this._config) {
       return;
     }
@@ -215,6 +216,7 @@ export class WorkerMain extends ProcessRunner {
         const tests = suite.allTests();
         for (let i = 0; i < tests.length; i++) {
           // Do not run tests after full cleanup, because we are entirely done.
+          // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
           if (this._isStopped && this._didRunFullCleanup) {
             break;
           }
@@ -362,6 +364,7 @@ export class WorkerMain extends ProcessRunner {
         testFunctionParams = await this._fixtureRunner.resolveParametersForFunction(test.fn, testInfo, 'test', { type: 'test' });
       });
 
+      // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
       if (testFunctionParams === null) {
         // Fixture setup failed or was skipped, we should not run the test now.
         return;
diff --git a/packages/recorder/src/recorder.tsx b/packages/recorder/src/recorder.tsx
index 7f092b6c6b..4f2b25040a 100644
--- a/packages/recorder/src/recorder.tsx
+++ b/packages/recorder/src/recorder.tsx
@@ -164,7 +164,7 @@ export const Recorder: React.FC<RecorderProps> = ({
         window.dispatch({ event: 'setMode', params: { mode: mode === 'assertingSnapshot' ? 'recording' : 'assertingSnapshot' } });
       }}></ToolbarButton>
       <ToolbarSeparator />
-      <ToolbarButton icon='files' title='Copy' disabled={!source || !source.text} onClick={() => {
+      <ToolbarButton icon='files' title='Copy' disabled={!source.text} onClick={() => {
         copy(source.text);
       }}></ToolbarButton>
       <ToolbarButton icon='debug-continue' title='Resume (F8)' ariaLabel='Resume' disabled={!paused} onClick={() => {
@@ -182,7 +182,7 @@ export const Recorder: React.FC<RecorderProps> = ({
         setSelectedFileId(fileId);
         window.dispatch({ event: 'fileChanged', params: { file: fileId } });
       }} />
-      <ToolbarButton icon='clear-all' title='Clear' disabled={!source || !source.text} onClick={() => {
+      <ToolbarButton icon='clear-all' title='Clear' disabled={!source.text} onClick={() => {
         window.dispatch({ event: 'clear' });
       }}></ToolbarButton>
       <ToolbarButton icon='color-mode' title='Toggle color mode' toggled={false} onClick={() => toggleTheme()}></ToolbarButton>
diff --git a/packages/recorder/src/recorderTypes.ts b/packages/recorder/src/recorderTypes.ts
index 4822dda46f..7c6b637e8f 100644
--- a/packages/recorder/src/recorderTypes.ts
+++ b/packages/recorder/src/recorderTypes.ts
@@ -43,7 +43,8 @@ export type EventData = {
     | 'pause'
     | 'setMode'
     | 'highlightRequested'
-    | 'fileChanged';
+    | 'fileChanged'
+    | 'runTask';
   params: any;
 };
 
diff --git a/packages/trace-viewer/bundle.ts b/packages/trace-viewer/bundle.ts
index 709d11ff7d..ebcae02c9f 100644
--- a/packages/trace-viewer/bundle.ts
+++ b/packages/trace-viewer/bundle.ts
@@ -21,6 +21,7 @@ export function bundle(): Plugin {
     name: 'playwright-bundle',
     transformIndexHtml: {
       handler(html, ctx) {
+        // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
         if (!ctx || !ctx.bundle) {
           return html;
         }
diff --git a/packages/trace-viewer/src/index.tsx b/packages/trace-viewer/src/index.tsx
index 808cf70e9a..2efeeb7e86 100644
--- a/packages/trace-viewer/src/index.tsx
+++ b/packages/trace-viewer/src/index.tsx
@@ -26,6 +26,7 @@ import { WorkbenchLoader } from './ui/workbenchLoader';
     if (window.location.href.includes('isUnderTest=true')) {
       await new Promise(f => setTimeout(f, 1000));
     }
+    // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
     if (!navigator.serviceWorker) {
       throw new Error(`Service workers are not supported.\nMake sure to serve the Trace Viewer (${window.location}) via HTTPS or localhost.`);
     }
diff --git a/packages/trace-viewer/src/recorder.tsx b/packages/trace-viewer/src/recorder.tsx
index 7f645c348f..4a959150f0 100644
--- a/packages/trace-viewer/src/recorder.tsx
+++ b/packages/trace-viewer/src/recorder.tsx
@@ -24,6 +24,7 @@ import { RecorderView } from './ui/recorder/recorderView';
   applyTheme();
 
   if (window.location.protocol !== 'file:') {
+    // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
     if (!navigator.serviceWorker) {
       throw new Error(`Service workers are not supported.\nMake sure to serve the Recorder (${window.location}) via HTTPS or localhost.`);
     }
diff --git a/packages/trace-viewer/src/sw/snapshotRenderer.ts b/packages/trace-viewer/src/sw/snapshotRenderer.ts
index 4f30895500..5d83c82f19 100644
--- a/packages/trace-viewer/src/sw/snapshotRenderer.ts
+++ b/packages/trace-viewer/src/sw/snapshotRenderer.ts
@@ -358,6 +358,7 @@ function snapshotScript(viewport: ViewportSize, ...targetIds: (string | undefine
 
       {
         const body = root.querySelector(`body[__playwright_custom_elements__]`);
+        // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
         if (body && window.customElements) {
           const customElements = (body.getAttribute('__playwright_custom_elements__') || '').split(',');
           for (const elementName of customElements) {
@@ -415,6 +416,7 @@ frameBoundingRectsInfo.frames.get(element)!.scrollLeft = element.scrollTop;
         const pointY = +search.get('pointY')!;
         const hasInputTarget = search.has('hasInputTarget');
         const hasTargetElements = targetElements.length > 0;
+        // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
         const roots = document.documentElement ? [document.documentElement] : [];
         for (const target of (hasTargetElements ? targetElements : roots)) {
           const pointElement = document.createElement('x-pw-pointer');
diff --git a/packages/trace-viewer/src/ui/callTab.tsx b/packages/trace-viewer/src/ui/callTab.tsx
index f3f87c4be6..12221402cd 100644
--- a/packages/trace-viewer/src/ui/callTab.tsx
+++ b/packages/trace-viewer/src/ui/callTab.tsx
@@ -131,6 +131,7 @@ function parseSerializedValue(value: SerializedValue, handles: any[] | undefined
     if (value.v === '-Infinity') {
       return -Infinity;
     }
+    // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
     if (value.v === '-0') {
       return -0;
     }
diff --git a/packages/trace-viewer/src/ui/consoleTab.tsx b/packages/trace-viewer/src/ui/consoleTab.tsx
index 5761242fa1..0001e63a48 100644
--- a/packages/trace-viewer/src/ui/consoleTab.tsx
+++ b/packages/trace-viewer/src/ui/consoleTab.tsx
@@ -202,6 +202,7 @@ function format(args: { preview: string, value: any }[]): JSX.Element[] {
     } else if (specifier === 'c') {
       tokens = [];
       const format = tail[argIndex++];
+      // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
       const styleObject = format ? parseCSSStyle(format.preview) : {};
       formatted.push(<span style={styleObject}>{tokens}</span>);
     }
diff --git a/packages/trace-viewer/src/ui/filmStrip.tsx b/packages/trace-viewer/src/ui/filmStrip.tsx
index b8bcbdc040..d111e1932f 100644
--- a/packages/trace-viewer/src/ui/filmStrip.tsx
+++ b/packages/trace-viewer/src/ui/filmStrip.tsx
@@ -58,6 +58,7 @@ export const FilmStrip: React.FunctionComponent<{
       width: Math.min(800, (window.innerWidth / 2) | 0),
       height: Math.min(800, (window.innerHeight / 2) | 0),
     };
+    // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
     previewSize = previewImage ? inscribe({ width: previewImage.width, height: previewImage.height }, fitInto) : undefined;
   }
 
diff --git a/packages/trace-viewer/src/ui/modelUtil.ts b/packages/trace-viewer/src/ui/modelUtil.ts
index 75d5ebcf16..3d694533d2 100644
--- a/packages/trace-viewer/src/ui/modelUtil.ts
+++ b/packages/trace-viewer/src/ui/modelUtil.ts
@@ -115,7 +115,7 @@ export class MultiTraceModel {
 
   private _errorDescriptorsFromActions(): ErrorDescription[] {
     const errors: ErrorDescription[] = [];
-    for (const action of this.actions || []) {
+    for (const action of this.actions) {
       if (!action.error?.message) {
         continue;
       }
@@ -130,7 +130,7 @@ export class MultiTraceModel {
 
   private _errorDescriptorsFromTestRunner(): ErrorDescription[] {
     const errors: ErrorDescription[] = [];
-    for (const error of this.errors || []) {
+    for (const error of this.errors) {
       if (!error.message) {
         continue;
       }
@@ -396,13 +396,14 @@ export function stats(action: ActionTraceEvent): { errors: number, warnings: num
 }
 
 export function eventsForAction(action: ActionTraceEvent): (trace.EventTraceEvent | trace.ConsoleMessageTraceEvent)[] {
-  let result: (trace.EventTraceEvent | trace.ConsoleMessageTraceEvent)[] = (action as any)[eventsSymbol];
+  let result = (action as any)[eventsSymbol] as Array<trace.EventTraceEvent | trace.ConsoleMessageTraceEvent> | undefined;
   if (result) {
     return result;
   }
 
   const nextAction = nextInContext(action);
   result = context(action).events.filter(event => {
+    // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
     return event.time >= action.startTime && (!nextAction || event.time < nextAction.startTime);
   });
   (action as any)[eventsSymbol] = result;
diff --git a/packages/trace-viewer/src/ui/networkTab.tsx b/packages/trace-viewer/src/ui/networkTab.tsx
index 8e57c91bb0..4428b3251f 100644
--- a/packages/trace-viewer/src/ui/networkTab.tsx
+++ b/packages/trace-viewer/src/ui/networkTab.tsx
@@ -264,6 +264,7 @@ class ContextIdMap {
 
   private _apiRequestContextId(resource: Entry): string {
     const contextEntry = context(resource);
+    // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
     if (!contextEntry) {
       return '';
     }
diff --git a/packages/trace-viewer/src/ui/recorder/actionListView.tsx b/packages/trace-viewer/src/ui/recorder/actionListView.tsx
index 8e9fa0df45..b7517d215a 100644
--- a/packages/trace-viewer/src/ui/recorder/actionListView.tsx
+++ b/packages/trace-viewer/src/ui/recorder/actionListView.tsx
@@ -50,6 +50,7 @@ export const ActionListView: React.FC<{
 
 export const renderAction = (sdkLanguage: Language, action: actionTypes.ActionInContext) => {
   const { method, apiName, params } = traceParamsForAction(action);
+  // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
   const locator = params.selector ? asLocator(sdkLanguage || 'javascript', params.selector) : undefined;
 
   return <>
diff --git a/packages/trace-viewer/src/ui/snapshotTab.tsx b/packages/trace-viewer/src/ui/snapshotTab.tsx
index 449b7fc55b..0450df6988 100644
--- a/packages/trace-viewer/src/ui/snapshotTab.tsx
+++ b/packages/trace-viewer/src/ui/snapshotTab.tsx
@@ -322,7 +322,7 @@ export function collectSnapshots(action: ActionTraceEvent | undefined): Snapshot
 
   // if the action has no beforeSnapshot, use the last available afterSnapshot.
   let beforeSnapshot: Snapshot | undefined = action.beforeSnapshot ? { action, snapshotName: action.beforeSnapshot } : undefined;
-  let a = action;
+  let a = action as ActionTraceEvent | undefined;
   while (!beforeSnapshot && a) {
     a = prevInList(a);
     beforeSnapshot = a.afterSnapshot ? { action: a, snapshotName: a.afterSnapshot } : undefined;
diff --git a/packages/trace-viewer/src/ui/uiModeTraceView.tsx b/packages/trace-viewer/src/ui/uiModeTraceView.tsx
index 1acb69a780..22dca6992b 100644
--- a/packages/trace-viewer/src/ui/uiModeTraceView.tsx
+++ b/packages/trace-viewer/src/ui/uiModeTraceView.tsx
@@ -53,7 +53,7 @@ export const TraceView: React.FC<{
     }
 
     // Test finished.
-    const attachment = result && result.duration >= 0 && result.attachments.find(a => a.name === 'trace');
+    const attachment = result.duration >= 0 && result.attachments.find(a => a.name === 'trace');
     if (attachment && attachment.path) {
       loadSingleTraceFile(attachment.path).then(model => setModel({ model, isLive: false }));
       return;
diff --git a/packages/trace-viewer/src/ui/uiModeView.tsx b/packages/trace-viewer/src/ui/uiModeView.tsx
index 1eab9901a5..fd8cf7204e 100644
--- a/packages/trace-viewer/src/ui/uiModeView.tsx
+++ b/packages/trace-viewer/src/ui/uiModeView.tsx
@@ -168,6 +168,7 @@ export const UIModeView: React.FC<{}> = ({
         throttleTimer = undefined;
         if (immediate) {
           setTestModel(teleSuiteUpdater.asModel());
+          // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
         } else if (!throttleTimer) {
           throttleTimer = setTimeout(() => {
             setTestModel(teleSuiteUpdater.asModel());
@@ -284,6 +285,7 @@ export const UIModeView: React.FC<{}> = ({
 
       // Clear test results.
       {
+        // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
         for (const test of testModel.rootSuite.allTests() || []) {
           if (testIds.has(test.id)) {
             test.results = [];
@@ -312,6 +314,7 @@ export const UIModeView: React.FC<{}> = ({
         trace: 'on',
       });
       // Clear pending tests in case of interrupt.
+      // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
       for (const test of testModel.rootSuite.allTests() || []) {
         if (test.results[0]?.duration === -1) {
           test.results = [];
@@ -525,6 +528,7 @@ export const UIModeView: React.FC<{}> = ({
           setFilterText={setFilterText}
           onRevealSource={onRevealSource}
         />
+        {/* eslint-disable-next-line @typescript-eslint/no-unnecessary-condition */}
         {showTestingOptions && <>
           <Toolbar noShadow={true} noMinHeight={true} className='settings-toolbar' onClick={() => setTestingOptionsVisible(!testingOptionsVisible)}>
             <span
diff --git a/packages/trace-viewer/src/uiMode.tsx b/packages/trace-viewer/src/uiMode.tsx
index c4186a0006..e5c7e59840 100644
--- a/packages/trace-viewer/src/uiMode.tsx
+++ b/packages/trace-viewer/src/uiMode.tsx
@@ -26,6 +26,7 @@ import { UIModeView } from './ui/uiModeView';
     if (window.location.href.includes('isUnderTest=true')) {
       await new Promise(f => setTimeout(f, 1000));
     }
+    // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
     if (!navigator.serviceWorker) {
       throw new Error(`Service workers are not supported.\nMake sure to serve the website (${window.location}) via HTTPS or localhost.`);
     }
diff --git a/packages/web/src/components/codeMirrorWrapper.tsx b/packages/web/src/components/codeMirrorWrapper.tsx
index d64773d4d1..f7bbc2dfb2 100644
--- a/packages/web/src/components/codeMirrorWrapper.tsx
+++ b/packages/web/src/components/codeMirrorWrapper.tsx
@@ -190,7 +190,7 @@ export const CodeMirrorWrapper: React.FC<SourceProps> = ({
       codemirror.scrollIntoView({ line: Math.max(0, revealLine - 1), ch: 0 }, 50);
     }
 
-    let changeListener: () => void | undefined;
+    let changeListener: (() => void | undefined) | undefined;
     if (onChange) {
       changeListener = () => onChange(codemirror.getValue());
       codemirror.on('change', changeListener);
diff --git a/packages/web/src/components/splitView.tsx b/packages/web/src/components/splitView.tsx
index 5833e44031..7490ca8bf4 100644
--- a/packages/web/src/components/splitView.tsx
+++ b/packages/web/src/components/splitView.tsx
@@ -52,12 +52,12 @@ export const SplitView: React.FC<SplitViewProps> = ({
   let size: number;
   if (orientation === 'vertical') {
     size = vSize / window.devicePixelRatio;
-    if (measure && measure.height < size) {
+    if (measure.height < size) {
       size = measure.height - 10;
     }
   } else {
     size = hSize / window.devicePixelRatio;
-    if (measure && measure.width < size) {
+    if (measure.width < size) {
       size = measure.width - 10;
     }
   }
diff --git a/packages/web/src/components/treeView.tsx b/packages/web/src/components/treeView.tsx
index 1f77066ae5..dffd429680 100644
--- a/packages/web/src/components/treeView.tsx
+++ b/packages/web/src/components/treeView.tsx
@@ -235,7 +235,7 @@ export function TreeItemHeader<T extends TreeItem>({
   isKeyboardNavigation,
   setIsKeyboardNavigation }: TreeItemHeaderProps<T>) {
   const groupId = React.useId();
-  const itemRef = React.useRef(null);
+  const itemRef = React.useRef<HTMLDivElement>(null);
 
   React.useEffect(() => {
     if (selectedItem === item && isKeyboardNavigation && itemRef.current) {
diff --git a/packages/web/src/shared/resizeView.tsx b/packages/web/src/shared/resizeView.tsx
index 72b58882df..984313d77f 100644
--- a/packages/web/src/shared/resizeView.tsx
+++ b/packages/web/src/shared/resizeView.tsx
@@ -68,6 +68,7 @@ export const ResizeView: React.FC<{
       onPaneMouseMove={event => {
         if (!event.buttons) {
           setResizing(null);
+          // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
         } else if (resizing) {
           const delta = orientation === 'horizontal' ? event.clientX - resizing.clientX : event.clientY - resizing.clientY;
           const newOffset = resizing.offset + delta;
diff --git a/packages/web/src/theme.ts b/packages/web/src/theme.ts
index b709daef60..b80924a5bb 100644
--- a/packages/web/src/theme.ts
+++ b/packages/web/src/theme.ts
@@ -51,9 +51,7 @@ export function toggleTheme() {
   const oldTheme = currentTheme();
   const newTheme = oldTheme === 'dark-mode' ? 'light-mode' : 'dark-mode';
 
-  if (oldTheme) {
-    document.body.classList.remove(oldTheme);
-  }
+  document.body.classList.remove(oldTheme);
   document.body.classList.add(newTheme);
   settings.setString('theme', newTheme);
   for (const listener of listeners) {