chore: use channel traits (#10389)

packages/playwright-core/src/browserServerImpl.ts

@@ -100,7 +100,8 @@ export class BrowserServerLauncherImpl implements BrowserServerLauncher {
 }
 
 // This class implements multiplexing browser dispatchers over a single Browser instance.
-class ConnectedBrowserDispatcher extends Dispatcher<Browser, channels.BrowserInitializer, channels.BrowserEvents> implements channels.BrowserChannel {
+class ConnectedBrowserDispatcher extends Dispatcher<Browser, channels.BrowserChannel> implements channels.BrowserChannel {
+  _type_Browser = true;
   private _contexts = new Set<BrowserContext>();
   private _selectors: Selectors;
 

packages/playwright-core/src/client/android.ts

@@ -30,7 +30,7 @@ import { EventEmitter } from 'events';
 type Direction = 'down' | 'up' | 'left' | 'right';
 type SpeedOptions = { speed?: number };
 
-export class Android extends ChannelOwner<channels.AndroidChannel, channels.AndroidInitializer> implements api.Android {
+export class Android extends ChannelOwner<channels.AndroidChannel> implements api.Android {
   readonly _timeoutSettings: TimeoutSettings;
 
   static from(android: channels.AndroidChannel): Android {
@@ -55,7 +55,7 @@ export class Android extends ChannelOwner<channels.AndroidChannel, channels.Andr
   }
 }
 
-export class AndroidDevice extends ChannelOwner<channels.AndroidDeviceChannel, channels.AndroidDeviceInitializer> implements api.AndroidDevice {
+export class AndroidDevice extends ChannelOwner<channels.AndroidDeviceChannel> implements api.AndroidDevice {
   readonly _timeoutSettings: TimeoutSettings;
   private _webViews = new Map<number, AndroidWebView>();
 
@@ -249,7 +249,7 @@ export class AndroidDevice extends ChannelOwner<channels.AndroidDeviceChannel, c
   }
 }
 
-export class AndroidSocket extends ChannelOwner<channels.AndroidSocketChannel, channels.AndroidSocketInitializer> implements api.AndroidSocket {
+export class AndroidSocket extends ChannelOwner<channels.AndroidSocketChannel> implements api.AndroidSocket {
   static from(androidDevice: channels.AndroidSocketChannel): AndroidSocket {
     return (androidDevice as any)._object;
   }

packages/playwright-core/src/client/artifact.ts

@@ -21,7 +21,7 @@ import { mkdirIfNeeded } from '../utils/utils';
 import { ChannelOwner } from './channelOwner';
 import { Readable } from 'stream';
 
-export class Artifact extends ChannelOwner<channels.ArtifactChannel, channels.ArtifactInitializer> {
+export class Artifact extends ChannelOwner<channels.ArtifactChannel> {
   static from(channel: channels.ArtifactChannel): Artifact {
     return (channel as any)._object;
   }

packages/playwright-core/src/client/browser.ts

@@ -25,7 +25,7 @@ import * as api from '../../types/types';
 import { CDPSession } from './cdpSession';
 import type { BrowserType } from './browserType';
 
-export class Browser extends ChannelOwner<channels.BrowserChannel, channels.BrowserInitializer> implements api.Browser {
+export class Browser extends ChannelOwner<channels.BrowserChannel> implements api.Browser {
   readonly _contexts = new Set<BrowserContext>();
   private _isConnected = true;
   private _closedPromise: Promise<void>;

packages/playwright-core/src/client/browserContext.ts

@@ -39,7 +39,7 @@ import { Artifact } from './artifact';
 import { APIRequestContext } from './fetch';
 import { createInstrumentation } from './clientInstrumentation';
 
-export class BrowserContext extends ChannelOwner<channels.BrowserContextChannel, channels.BrowserContextInitializer> implements api.BrowserContext {
+export class BrowserContext extends ChannelOwner<channels.BrowserContextChannel> implements api.BrowserContext {
   _pages = new Set<Page>();
   private _routes: network.RouteHandler[] = [];
   readonly _browser: Browser | null = null;

packages/playwright-core/src/client/browserType.ts

@@ -41,7 +41,7 @@ export interface BrowserServer extends api.BrowserServer {
   kill(): Promise<void>;
 }
 
-export class BrowserType extends ChannelOwner<channels.BrowserTypeChannel, channels.BrowserTypeInitializer> implements api.BrowserType {
+export class BrowserType extends ChannelOwner<channels.BrowserTypeChannel> implements api.BrowserType {
   _serverLauncher?: BrowserServerLauncher;
   _contexts = new Set<BrowserContext>();
   _playwright!: Playwright;

packages/playwright-core/src/client/cdpSession.ts

@@ -19,7 +19,7 @@ import { ChannelOwner } from './channelOwner';
 import { Protocol } from '../server/chromium/protocol';
 import * as api from '../../types/types';
 
-export class CDPSession extends ChannelOwner<channels.CDPSessionChannel, channels.CDPSessionInitializer> implements api.CDPSession {
+export class CDPSession extends ChannelOwner<channels.CDPSessionChannel> implements api.CDPSession {
   static from(cdpSession: channels.CDPSessionChannel): CDPSession {
     return (cdpSession as any)._object;
   }

packages/playwright-core/src/client/channelOwner.ts

@@ -24,7 +24,7 @@ import { ClientInstrumentation } from './clientInstrumentation';
 import type { Connection } from './connection';
 import type { Logger } from './types';
 
-export abstract class ChannelOwner<T extends channels.Channel = channels.Channel, Initializer = {}> extends EventEmitter {
+export abstract class ChannelOwner<T extends channels.Channel = channels.Channel> extends EventEmitter {
   readonly _connection: Connection;
   private _parent: ChannelOwner | undefined;
   private _objects = new Map<string, ChannelOwner>();
@@ -32,11 +32,11 @@ export abstract class ChannelOwner<T extends channels.Channel = channels.Channel
   readonly _type: string;
   readonly _guid: string;
   readonly _channel: T;
-  readonly _initializer: Initializer;
+  readonly _initializer: channels.InitializerTraits<T>;
   _logger: Logger | undefined;
   _instrumentation: ClientInstrumentation | undefined;
 
-  constructor(parent: ChannelOwner | Connection, type: string, guid: string, initializer: Initializer, instrumentation?: ClientInstrumentation) {
+  constructor(parent: ChannelOwner | Connection, type: string, guid: string, initializer: channels.InitializerTraits<T>, instrumentation?: ClientInstrumentation) {
     super();
     this.setMaxListeners(0);
     this._connection = parent instanceof ChannelOwner ? parent._connection : parent;

packages/playwright-core/src/client/connection.ts

@@ -41,7 +41,7 @@ import { EventEmitter } from 'events';
 import { JsonPipe } from './jsonPipe';
 import { APIRequestContext } from './fetch';
 
-class Root extends ChannelOwner<channels.RootChannel, {}> {
+class Root extends ChannelOwner<channels.RootChannel> {
   constructor(connection: Connection) {
     super(connection, 'Root', '', {});
   }
@@ -142,7 +142,7 @@ export class Connection extends EventEmitter {
     const object = this._objects.get(guid);
     if (!object)
       throw new Error(`Cannot find object to emit "${method}": ${guid}`);
-    object._channel.emit(method, object._type === 'JsonPipe' ? params : this._replaceGuidsWithChannels(params));
+    (object._channel as any).emit(method, object._type === 'JsonPipe' ? params : this._replaceGuidsWithChannels(params));
   }
 
   close(errorMessage: string = 'Connection closed') {
@@ -173,7 +173,7 @@ export class Connection extends EventEmitter {
     const parent = this._objects.get(parentGuid);
     if (!parent)
       throw new Error(`Cannot find parent object ${parentGuid} to create ${guid}`);
-    let result: ChannelOwner<any, any>;
+    let result: ChannelOwner<any>;
     initializer = this._replaceGuidsWithChannels(initializer);
     switch (type) {
       case 'Android':

packages/playwright-core/src/client/consoleMessage.ts

@@ -22,7 +22,7 @@ import * as api from '../../types/types';
 
 type ConsoleMessageLocation = channels.ConsoleMessageInitializer['location'];
 
-export class ConsoleMessage extends ChannelOwner<channels.ConsoleMessageChannel, channels.ConsoleMessageInitializer> implements api.ConsoleMessage {
+export class ConsoleMessage extends ChannelOwner<channels.ConsoleMessageChannel> implements api.ConsoleMessage {
   static from(message: channels.ConsoleMessageChannel): ConsoleMessage {
     return (message as any)._object;
   }

packages/playwright-core/src/client/dialog.ts

@@ -18,7 +18,7 @@ import * as channels from '../protocol/channels';
 import { ChannelOwner } from './channelOwner';
 import * as api from '../../types/types';
 
-export class Dialog extends ChannelOwner<channels.DialogChannel, channels.DialogInitializer> implements api.Dialog {
+export class Dialog extends ChannelOwner<channels.DialogChannel> implements api.Dialog {
   static from(dialog: channels.DialogChannel): Dialog {
     return (dialog as any)._object;
   }

packages/playwright-core/src/client/electron.ts

@@ -36,7 +36,7 @@ type ElectronOptions = Omit<channels.ElectronLaunchOptions, 'env'|'extraHTTPHead
 
 type ElectronAppType = typeof import('electron');
 
-export class Electron extends ChannelOwner<channels.ElectronChannel, channels.ElectronInitializer> implements api.Electron {
+export class Electron extends ChannelOwner<channels.ElectronChannel> implements api.Electron {
   static from(electron: channels.ElectronChannel): Electron {
     return (electron as any)._object;
   }
@@ -57,7 +57,7 @@ export class Electron extends ChannelOwner<channels.ElectronChannel, channels.El
   }
 }
 
-export class ElectronApplication extends ChannelOwner<channels.ElectronApplicationChannel, channels.ElectronApplicationInitializer> implements api.ElectronApplication {
+export class ElectronApplication extends ChannelOwner<channels.ElectronApplicationChannel> implements api.ElectronApplication {
   private _context: BrowserContext;
   private _windows = new Set<Page>();
   private _timeoutSettings = new TimeoutSettings();

packages/playwright-core/src/client/fetch.ts

@@ -70,7 +70,7 @@ export class APIRequest implements api.APIRequest {
   }
 }
 
-export class APIRequestContext extends ChannelOwner<channels.APIRequestContextChannel, channels.APIRequestContextInitializer> implements api.APIRequestContext {
+export class APIRequestContext extends ChannelOwner<channels.APIRequestContextChannel> implements api.APIRequestContext {
   static from(channel: channels.APIRequestContextChannel): APIRequestContext {
     return (channel as any)._object;
   }

packages/playwright-core/src/client/frame.ts

@@ -38,7 +38,7 @@ export type WaitForNavigationOptions = {
   url?: URLMatch,
 };
 
-export class Frame extends ChannelOwner<channels.FrameChannel, channels.FrameInitializer> implements api.Frame {
+export class Frame extends ChannelOwner<channels.FrameChannel> implements api.Frame {
   _eventEmitter: EventEmitter;
   _loadStates: Set<LifecycleEvent>;
   _parentFrame: Frame | null = null;

packages/playwright-core/src/client/jsHandle.ts

@@ -20,7 +20,7 @@ import { parseSerializedValue, serializeValue } from '../protocol/serializers';
 import * as api from '../../types/types';
 import * as structs from '../../types/structs';
 
-export class JSHandle<T = any> extends ChannelOwner<channels.JSHandleChannel, channels.JSHandleInitializer> implements api.JSHandle {
+export class JSHandle<T = any> extends ChannelOwner<channels.JSHandleChannel> implements api.JSHandle {
   private _preview: string;
 
   static from(handle: channels.JSHandleChannel): JSHandle {

packages/playwright-core/src/client/jsonPipe.ts

@@ -17,7 +17,7 @@
 import * as channels from '../protocol/channels';
 import { ChannelOwner } from './channelOwner';
 
-export class JsonPipe extends ChannelOwner<channels.JsonPipeChannel, channels.JsonPipeInitializer> {
+export class JsonPipe extends ChannelOwner<channels.JsonPipeChannel> {
   static from(jsonPipe: channels.JsonPipeChannel): JsonPipe {
     return (jsonPipe as any)._object;
   }

packages/playwright-core/src/client/network.ts

@@ -55,7 +55,7 @@ export type SetNetworkCookieParam = {
   sameSite?: 'Strict' | 'Lax' | 'None'
 };
 
-export class Request extends ChannelOwner<channels.RequestChannel, channels.RequestInitializer> implements api.Request {
+export class Request extends ChannelOwner<channels.RequestChannel> implements api.Request {
   private _redirectedFrom: Request | null = null;
   private _redirectedTo: Request | null = null;
   _failureText: string | null = null;
@@ -215,7 +215,7 @@ export class Request extends ChannelOwner<channels.RequestChannel, channels.Requ
   }
 }
 
-export class Route extends ChannelOwner<channels.RouteChannel, channels.RouteInitializer> implements api.Route {
+export class Route extends ChannelOwner<channels.RouteChannel> implements api.Route {
   static from(route: channels.RouteChannel): Route {
     return (route as any)._object;
   }
@@ -334,7 +334,7 @@ export type RequestSizes = {
   responseHeadersSize: number;
 };
 
-export class Response extends ChannelOwner<channels.ResponseChannel, channels.ResponseInitializer> implements api.Response {
+export class Response extends ChannelOwner<channels.ResponseChannel> implements api.Response {
   private _provisionalHeaders: RawHeaders;
   private _actualHeadersPromise: Promise<RawHeaders> | undefined;
   private _request: Request;
@@ -445,7 +445,7 @@ export class Response extends ChannelOwner<channels.ResponseChannel, channels.Re
   }
 }
 
-export class WebSocket extends ChannelOwner<channels.WebSocketChannel, channels.WebSocketInitializer> implements api.WebSocket {
+export class WebSocket extends ChannelOwner<channels.WebSocketChannel> implements api.WebSocket {
   private _page: Page;
   private _isClosed: boolean;
 

packages/playwright-core/src/client/page.ts

@@ -62,7 +62,7 @@ type PDFOptions = Omit<channels.PagePdfParams, 'width' | 'height' | 'margin'> &
 };
 type Listener = (...args: any[]) => void;
 
-export class Page extends ChannelOwner<channels.PageChannel, channels.PageInitializer> implements api.Page {
+export class Page extends ChannelOwner<channels.PageChannel> implements api.Page {
   private _browserContext: BrowserContext;
   _ownedContext: BrowserContext | undefined;
 
@@ -96,7 +96,7 @@ export class Page extends ChannelOwner<channels.PageChannel, channels.PageInitia
 
   constructor(parent: ChannelOwner, type: string, guid: string, initializer: channels.PageInitializer) {
     super(parent, type, guid, initializer);
-    this._browserContext = parent as BrowserContext;
+    this._browserContext = parent as unknown as BrowserContext;
     this._timeoutSettings = new TimeoutSettings(this._browserContext._timeoutSettings);
 
     this.accessibility = new Accessibility(this._channel);
@@ -698,7 +698,7 @@ export class Page extends ChannelOwner<channels.PageChannel, channels.PageInitia
   }
 }
 
-export class BindingCall extends ChannelOwner<channels.BindingCallChannel, channels.BindingCallInitializer> {
+export class BindingCall extends ChannelOwner<channels.BindingCallChannel> {
   static from(channel: channels.BindingCallChannel): BindingCall {
     return (channel as any)._object;
   }

packages/playwright-core/src/client/playwright.ts

@@ -39,7 +39,7 @@ type DeviceDescriptor = {
 };
 type Devices = { [name: string]: DeviceDescriptor };
 
-export class Playwright extends ChannelOwner<channels.PlaywrightChannel, channels.PlaywrightInitializer> {
+export class Playwright extends ChannelOwner<channels.PlaywrightChannel> {
   readonly _android: Android;
   readonly _electron: Electron;
   readonly chromium: BrowserType;

packages/playwright-core/src/client/selectors.ts

@@ -45,7 +45,7 @@ export class Selectors implements api.Selectors {
   }
 }
 
-export class SelectorsOwner extends ChannelOwner<channels.SelectorsChannel, channels.SelectorsInitializer> {
+export class SelectorsOwner extends ChannelOwner<channels.SelectorsChannel> {
   static from(browser: channels.SelectorsChannel): SelectorsOwner {
     return (browser as any)._object;
   }

packages/playwright-core/src/client/stream.ts

@@ -18,7 +18,7 @@ import { Readable } from 'stream';
 import * as channels from '../protocol/channels';
 import { ChannelOwner } from './channelOwner';
 
-export class Stream extends ChannelOwner<channels.StreamChannel, channels.StreamInitializer> {
+export class Stream extends ChannelOwner<channels.StreamChannel> {
   static from(Stream: channels.StreamChannel): Stream {
     return (Stream as any)._object;
   }

packages/playwright-core/src/client/worker.ts

@@ -23,7 +23,7 @@ import { BrowserContext } from './browserContext';
 import * as api from '../../types/types';
 import * as structs from '../../types/structs';
 
-export class Worker extends ChannelOwner<channels.WorkerChannel, channels.WorkerInitializer> implements api.Worker {
+export class Worker extends ChannelOwner<channels.WorkerChannel> implements api.Worker {
   _page: Page | undefined;  // Set for web workers.
   _context: BrowserContext | undefined;  // Set for service workers.
 

packages/playwright-core/src/dispatchers/androidDispatcher.ts

@@ -20,7 +20,8 @@ import * as channels from '../protocol/channels';
 import { BrowserContextDispatcher } from './browserContextDispatcher';
 import { CallMetadata } from '../server/instrumentation';
 
-export class AndroidDispatcher extends Dispatcher<Android, channels.AndroidInitializer, channels.AndroidEvents> implements channels.AndroidChannel {
+export class AndroidDispatcher extends Dispatcher<Android, channels.AndroidChannel> implements channels.AndroidChannel {
+  _type_Android = true;
   constructor(scope: DispatcherScope, android: Android) {
     super(scope, android, 'Android', {}, true);
   }
@@ -37,7 +38,9 @@ export class AndroidDispatcher extends Dispatcher<Android, channels.AndroidIniti
   }
 }
 
-export class AndroidDeviceDispatcher extends Dispatcher<AndroidDevice, channels.AndroidDeviceInitializer, channels.AndroidDeviceEvents> implements channels.AndroidDeviceChannel {
+export class AndroidDeviceDispatcher extends Dispatcher<AndroidDevice, channels.AndroidDeviceChannel> implements channels.AndroidDeviceChannel {
+  _type_EventTarget = true;
+  _type_AndroidDevice = true;
 
   static from(scope: DispatcherScope, device: AndroidDevice): AndroidDeviceDispatcher {
     const result = existingDispatcher<AndroidDeviceDispatcher>(device);
@@ -169,7 +172,9 @@ export class AndroidDeviceDispatcher extends Dispatcher<AndroidDevice, channels.
   }
 }
 
-export class AndroidSocketDispatcher extends Dispatcher<SocketBackend, channels.AndroidSocketInitializer, channels.AndroidSocketEvents> implements channels.AndroidSocketChannel {
+export class AndroidSocketDispatcher extends Dispatcher<SocketBackend, channels.AndroidSocketChannel> implements channels.AndroidSocketChannel {
+  _type_AndroidSocket = true;
+
   constructor(scope: DispatcherScope, socket: SocketBackend) {
     super(scope, socket, 'AndroidSocket', {}, true);
     socket.on('data', (data: Buffer) => this._dispatchEvent('data', { data: data.toString('base64') }));

packages/playwright-core/src/dispatchers/artifactDispatcher.ts

@@ -21,7 +21,8 @@ import fs from 'fs';
 import { mkdirIfNeeded } from '../utils/utils';
 import { Artifact } from '../server/artifact';
 
-export class ArtifactDispatcher extends Dispatcher<Artifact, channels.ArtifactInitializer, channels.ArtifactEvents> implements channels.ArtifactChannel {
+export class ArtifactDispatcher extends Dispatcher<Artifact, channels.ArtifactChannel> implements channels.ArtifactChannel {
+  _type_Artifact = true;
   constructor(scope: DispatcherScope, artifact: Artifact) {
     super(scope, artifact, 'Artifact', {
       absolutePath: artifact.localPath(),

packages/playwright-core/src/dispatchers/browserContextDispatcher.ts

@@ -28,7 +28,9 @@ import { ArtifactDispatcher } from './artifactDispatcher';
 import { Artifact } from '../server/artifact';
 import { Request, Response } from '../server/network';
 
-export class BrowserContextDispatcher extends Dispatcher<BrowserContext, channels.BrowserContextInitializer, channels.BrowserContextEvents> implements channels.BrowserContextChannel {
+export class BrowserContextDispatcher extends Dispatcher<BrowserContext, channels.BrowserContextChannel> implements channels.BrowserContextChannel {
+  _type_EventTarget = true;
+  _type_BrowserContext = true;
   private _context: BrowserContext;
 
   constructor(scope: DispatcherScope, context: BrowserContext) {

packages/playwright-core/src/dispatchers/browserDispatcher.ts

@@ -23,7 +23,8 @@ import { CRBrowser } from '../server/chromium/crBrowser';
 import { PageDispatcher } from './pageDispatcher';
 import { CallMetadata } from '../server/instrumentation';
 
-export class BrowserDispatcher extends Dispatcher<Browser, channels.BrowserInitializer, channels.BrowserEvents> implements channels.BrowserChannel {
+export class BrowserDispatcher extends Dispatcher<Browser, channels.BrowserChannel> implements channels.BrowserChannel {
+  _type_Browser = true;
   constructor(scope: DispatcherScope, browser: Browser) {
     super(scope, browser, 'Browser', { version: browser.version(), name: browser.options.name }, true);
     browser.on(Browser.Events.Disconnected, () => this._didClose());

packages/playwright-core/src/dispatchers/browserTypeDispatcher.ts

@@ -25,7 +25,8 @@ import { JsonPipeDispatcher } from '../dispatchers/jsonPipeDispatcher';
 import { getUserAgent, makeWaitForNextTask } from '../utils/utils';
 import { ManualPromise } from '../utils/async';
 
-export class BrowserTypeDispatcher extends Dispatcher<BrowserType, channels.BrowserTypeInitializer, channels.BrowserTypeEvents> implements channels.BrowserTypeChannel {
+export class BrowserTypeDispatcher extends Dispatcher<BrowserType, channels.BrowserTypeChannel> implements channels.BrowserTypeChannel {
+  _type_BrowserType = true;
   constructor(scope: DispatcherScope, browserType: BrowserType) {
     super(scope, browserType, 'BrowserType', {
       executablePath: browserType.executablePath(),

packages/playwright-core/src/dispatchers/cdpSessionDispatcher.ts

@@ -18,7 +18,9 @@ import { CRSession, CRSessionEvents } from '../server/chromium/crConnection';
 import * as channels from '../protocol/channels';
 import { Dispatcher, DispatcherScope } from './dispatcher';
 
-export class CDPSessionDispatcher extends Dispatcher<CRSession, channels.CDPSessionInitializer, channels.CDPSessionEvents> implements channels.CDPSessionChannel {
+export class CDPSessionDispatcher extends Dispatcher<CRSession, channels.CDPSessionChannel> implements channels.CDPSessionChannel {
+  _type_CDPSession = true;
+
   constructor(scope: DispatcherScope, crSession: CRSession) {
     super(scope, crSession, 'CDPSession', {}, true);
     crSession._eventListener = (method, params) => {

packages/playwright-core/src/dispatchers/consoleMessageDispatcher.ts

@@ -19,7 +19,8 @@ import * as channels from '../protocol/channels';
 import { Dispatcher, DispatcherScope } from './dispatcher';
 import { ElementHandleDispatcher } from './elementHandlerDispatcher';
 
-export class ConsoleMessageDispatcher extends Dispatcher<ConsoleMessage, channels.ConsoleMessageInitializer, channels.ConsoleMessageEvents> implements channels.ConsoleMessageChannel {
+export class ConsoleMessageDispatcher extends Dispatcher<ConsoleMessage, channels.ConsoleMessageChannel> implements channels.ConsoleMessageChannel {
+  _type_ConsoleMessage = true;
   constructor(scope: DispatcherScope, message: ConsoleMessage) {
     super(scope, message, 'ConsoleMessage', {
       type: message.type(),

packages/playwright-core/src/dispatchers/dialogDispatcher.ts

@@ -18,7 +18,8 @@ import { Dialog } from '../server/dialog';
 import * as channels from '../protocol/channels';
 import { Dispatcher, DispatcherScope } from './dispatcher';
 
-export class DialogDispatcher extends Dispatcher<Dialog, channels.DialogInitializer, channels.DialogEvents> implements channels.DialogChannel {
+export class DialogDispatcher extends Dispatcher<Dialog, channels.DialogChannel> implements channels.DialogChannel {
+  _type_Dialog = true;
   constructor(scope: DispatcherScope, dialog: Dialog) {
     super(scope, dialog, 'Dialog', {
       type: dialog.type(),

packages/playwright-core/src/dispatchers/dispatcher.ts

@@ -41,21 +41,21 @@ export function lookupNullableDispatcher<DispatcherType>(object: any | null): Di
   return object ? lookupDispatcher(object) : undefined;
 }
 
-export class Dispatcher<Type extends { guid: string }, Initializer, Events> extends EventEmitter implements channels.Channel {
+export class Dispatcher<Type extends { guid: string }, ChannelType> extends EventEmitter implements channels.Channel {
   private _connection: DispatcherConnection;
   private _isScope: boolean;
   // Parent is always "isScope".
-  private _parent: Dispatcher<any, any, {}> | undefined;
+  private _parent: Dispatcher<any, any> | undefined;
   // Only "isScope" channel owners have registered dispatchers inside.
-  private _dispatchers = new Map<string, Dispatcher<any, any, {}>>();
+  private _dispatchers = new Map<string, Dispatcher<any, any>>();
   protected _disposed = false;
 
   readonly _guid: string;
   readonly _type: string;
-  readonly _scope: Dispatcher<any, any, {}>;
+  readonly _scope: Dispatcher<any, any>;
   _object: Type;
 
-  constructor(parent: Dispatcher<any, any, {}> | DispatcherConnection, object: Type, type: string, initializer: Initializer, isScope?: boolean) {
+  constructor(parent: Dispatcher<any, any> | DispatcherConnection, object: Type, type: string, initializer: channels.InitializerTraits<Type>, isScope?: boolean) {
     super();
 
     this._connection = parent instanceof DispatcherConnection ? parent : parent._connection;
@@ -80,7 +80,7 @@ export class Dispatcher<Type extends { guid: string }, Initializer, Events> exte
       this._connection.sendMessageToClient(this._parent._guid, type, '__create__', { type, initializer, guid }, this._parent._object);
   }
 
-  _dispatchEvent<T extends keyof Events>(method: T, params?: Events[T]) {
+  _dispatchEvent<T extends keyof channels.EventsTraits<ChannelType>>(method: T, params?: channels.EventsTraits<ChannelType>[T]) {
     if (this._disposed) {
       if (isUnderTest())
         throw new Error(`${this._guid} is sending "${method}" event after being disposed`);
@@ -121,8 +121,8 @@ export class Dispatcher<Type extends { guid: string }, Initializer, Events> exte
   }
 }
 
-export type DispatcherScope = Dispatcher<any, any, {}>;
+export type DispatcherScope = Dispatcher<any, any>;
-export class Root extends Dispatcher<{ guid: '' }, {}, {}> {
+export class Root extends Dispatcher<{ guid: '' }, any> {
   private _initialized = false;
 
   constructor(connection: DispatcherConnection, private readonly createPlaywright?: (scope: DispatcherScope, options: channels.RootInitializeParams) => Promise<PlaywrightDispatcher>) {
@@ -140,7 +140,7 @@ export class Root extends Dispatcher<{ guid: '' }, {}, {}> {
 }
 
 export class DispatcherConnection {
-  readonly _dispatchers = new Map<string, Dispatcher<any, any, {}>>();
+  readonly _dispatchers = new Map<string, Dispatcher<any, any>>();
   onmessage = (message: object) => {};
   private _validateParams: (type: string, method: string, params: any) => any;
   private _validateMetadata: (metadata: any) => { stack?: channels.StackFrame[] };

packages/playwright-core/src/dispatchers/electronDispatcher.ts

@@ -22,7 +22,8 @@ import { PageDispatcher } from './pageDispatcher';
 import { parseArgument, serializeResult } from './jsHandleDispatcher';
 import { ElementHandleDispatcher } from './elementHandlerDispatcher';
 
-export class ElectronDispatcher extends Dispatcher<Electron, channels.ElectronInitializer, channels.ElectronEvents> implements channels.ElectronChannel {
+export class ElectronDispatcher extends Dispatcher<Electron, channels.ElectronChannel> implements channels.ElectronChannel {
+  _type_Electron = true;
   constructor(scope: DispatcherScope, electron: Electron) {
     super(scope, electron, 'Electron', {}, true);
   }
@@ -33,7 +34,10 @@ export class ElectronDispatcher extends Dispatcher<Electron, channels.ElectronIn
   }
 }
 
-export class ElectronApplicationDispatcher extends Dispatcher<ElectronApplication, channels.ElectronApplicationInitializer, channels.ElectronApplicationEvents> implements channels.ElectronApplicationChannel {
+export class ElectronApplicationDispatcher extends Dispatcher<ElectronApplication, channels.ElectronApplicationChannel> implements channels.ElectronApplicationChannel {
+  _type_EventTarget = true;
+  _type_ElectronApplication = true;
+
   constructor(scope: DispatcherScope, electronApplication: ElectronApplication) {
     super(scope, electronApplication, 'ElectronApplication', {
       context: new BrowserContextDispatcher(scope, electronApplication.context())

packages/playwright-core/src/dispatchers/elementHandlerDispatcher.ts

@@ -23,6 +23,8 @@ import { FrameDispatcher } from './frameDispatcher';
 import { CallMetadata } from '../server/instrumentation';
 
 export class ElementHandleDispatcher extends JSHandleDispatcher implements channels.ElementHandleChannel {
+  _type_ElementHandle = true;
+
   readonly _elementHandle: ElementHandle;
 
   static from(scope: DispatcherScope, handle: ElementHandle): ElementHandleDispatcher {

packages/playwright-core/src/dispatchers/frameDispatcher.ts

@@ -22,7 +22,8 @@ import { parseArgument, serializeResult } from './jsHandleDispatcher';
 import { ResponseDispatcher, RequestDispatcher } from './networkDispatchers';
 import { CallMetadata } from '../server/instrumentation';
 
-export class FrameDispatcher extends Dispatcher<Frame, channels.FrameInitializer, channels.FrameEvents> implements channels.FrameChannel {
+export class FrameDispatcher extends Dispatcher<Frame, channels.FrameChannel> implements channels.FrameChannel {
+  _type_Frame = true;
   private _frame: Frame;
 
   static from(scope: DispatcherScope, frame: Frame): FrameDispatcher {

packages/playwright-core/src/dispatchers/jsHandleDispatcher.ts

@@ -20,7 +20,8 @@ import { Dispatcher, DispatcherScope } from './dispatcher';
 import { ElementHandleDispatcher } from './elementHandlerDispatcher';
 import { parseSerializedValue, serializeValue } from '../protocol/serializers';
 
-export class JSHandleDispatcher extends Dispatcher<js.JSHandle, channels.JSHandleInitializer, channels.JSHandleEvents> implements channels.JSHandleChannel {
+export class JSHandleDispatcher extends Dispatcher<js.JSHandle, channels.JSHandleChannel> implements channels.JSHandleChannel {
+  _type_JSHandle = true;
 
   protected constructor(scope: DispatcherScope, jsHandle: js.JSHandle) {
     // Do not call this directly, use createHandle() instead.

packages/playwright-core/src/dispatchers/jsonPipeDispatcher.ts

@@ -19,7 +19,8 @@ import { Dispatcher, DispatcherScope } from './dispatcher';
 import { createGuid } from '../utils/utils';
 import { serializeError } from '../protocol/serializers';
 
-export class JsonPipeDispatcher extends Dispatcher<{ guid: string }, channels.JsonPipeInitializer, channels.JsonPipeEvents> implements channels.JsonPipeChannel {
+export class JsonPipeDispatcher extends Dispatcher<{ guid: string }, channels.JsonPipeChannel> implements channels.JsonPipeChannel {
+  _type_JsonPipe = true;
   constructor(scope: DispatcherScope) {
     super(scope, { guid: 'jsonPipe@' + createGuid() }, 'JsonPipe', {});
   }

packages/playwright-core/src/dispatchers/networkDispatchers.ts

@@ -21,7 +21,8 @@ import { Request, Response, Route, WebSocket } from '../server/network';
 import { Dispatcher, DispatcherScope, existingDispatcher, lookupNullableDispatcher } from './dispatcher';
 import { FrameDispatcher } from './frameDispatcher';
 
-export class RequestDispatcher extends Dispatcher<Request, channels.RequestInitializer, channels.RequestEvents> implements channels.RequestChannel {
+export class RequestDispatcher extends Dispatcher<Request, channels.RequestChannel> implements channels.RequestChannel {
+  _type_Request: boolean;
 
   static from(scope: DispatcherScope, request: Request): RequestDispatcher {
     const result = existingDispatcher<RequestDispatcher>(request);
@@ -44,6 +45,7 @@ export class RequestDispatcher extends Dispatcher<Request, channels.RequestIniti
       isNavigationRequest: request.isNavigationRequest(),
       redirectedFrom: RequestDispatcher.fromNullable(scope, request.redirectedFrom()),
     });
+    this._type_Request = true;
   }
 
   async rawRequestHeaders(params?: channels.RequestRawRequestHeadersParams): Promise<channels.RequestRawRequestHeadersResult> {
@@ -55,7 +57,8 @@ export class RequestDispatcher extends Dispatcher<Request, channels.RequestIniti
   }
 }
 
-export class ResponseDispatcher extends Dispatcher<Response, channels.ResponseInitializer, channels.ResponseEvents> implements channels.ResponseChannel {
+export class ResponseDispatcher extends Dispatcher<Response, channels.ResponseChannel> implements channels.ResponseChannel {
+  _type_Response = true;
 
   static from(scope: DispatcherScope, response: Response): ResponseDispatcher {
     const result = existingDispatcher<ResponseDispatcher>(response);
@@ -99,7 +102,8 @@ export class ResponseDispatcher extends Dispatcher<Response, channels.ResponseIn
   }
 }
 
-export class RouteDispatcher extends Dispatcher<Route, channels.RouteInitializer, channels.RouteEvents> implements channels.RouteChannel {
+export class RouteDispatcher extends Dispatcher<Route, channels.RouteChannel> implements channels.RouteChannel {
+  _type_Route = true;
 
   static from(scope: DispatcherScope, route: Route): RouteDispatcher {
     const result = existingDispatcher<RouteDispatcher>(route);
@@ -131,7 +135,10 @@ export class RouteDispatcher extends Dispatcher<Route, channels.RouteInitializer
   }
 }
 
-export class WebSocketDispatcher extends Dispatcher<WebSocket, channels.WebSocketInitializer, channels.WebSocketEvents> implements channels.WebSocketChannel {
+export class WebSocketDispatcher extends Dispatcher<WebSocket, channels.WebSocketChannel> implements channels.WebSocketChannel {
+  _type_EventTarget = true;
+  _type_WebSocket = true;
+
   constructor(scope: DispatcherScope, webSocket: WebSocket) {
     super(scope, webSocket, 'WebSocket', {
       url: webSocket.url(),
@@ -143,7 +150,9 @@ export class WebSocketDispatcher extends Dispatcher<WebSocket, channels.WebSocke
   }
 }
 
-export class APIRequestContextDispatcher extends Dispatcher<APIRequestContext, channels.APIRequestContextInitializer, channels.APIRequestContextEvents> implements channels.APIRequestContextChannel {
+export class APIRequestContextDispatcher extends Dispatcher<APIRequestContext, channels.APIRequestContextChannel> implements channels.APIRequestContextChannel {
+  _type_APIRequestContext = true;
+
   static from(scope: DispatcherScope, request: APIRequestContext): APIRequestContextDispatcher {
     const result = existingDispatcher<APIRequestContextDispatcher>(request);
     return result || new APIRequestContextDispatcher(scope, request);

packages/playwright-core/src/dispatchers/pageDispatcher.ts

@@ -35,7 +35,9 @@ import { ArtifactDispatcher } from './artifactDispatcher';
 import { Download } from '../server/download';
 import { createGuid } from '../utils/utils';
 
-export class PageDispatcher extends Dispatcher<Page, channels.PageInitializer, channels.PageEvents> implements channels.PageChannel {
+export class PageDispatcher extends Dispatcher<Page, channels.PageChannel> implements channels.PageChannel {
+  _type_EventTarget = true;
+  _type_Page = true;
   private _page: Page;
 
   static fromNullable(scope: DispatcherScope, page: Page | undefined): PageDispatcher | undefined {
@@ -253,7 +255,8 @@ export class PageDispatcher extends Dispatcher<Page, channels.PageInitializer, c
 }
 
 
-export class WorkerDispatcher extends Dispatcher<Worker, channels.WorkerInitializer, channels.WorkerEvents> implements channels.WorkerChannel {
+export class WorkerDispatcher extends Dispatcher<Worker, channels.WorkerChannel> implements channels.WorkerChannel {
+  _type_Worker = true;
   constructor(scope: DispatcherScope, worker: Worker) {
     super(scope, worker, 'Worker', {
       url: worker.url()
@@ -270,7 +273,8 @@ export class WorkerDispatcher extends Dispatcher<Worker, channels.WorkerInitiali
   }
 }
 
-export class BindingCallDispatcher extends Dispatcher<{ guid: string }, channels.BindingCallInitializer, channels.BindingCallEvents> implements channels.BindingCallChannel {
+export class BindingCallDispatcher extends Dispatcher<{ guid: string }, channels.BindingCallChannel> implements channels.BindingCallChannel {
+  _type_BindingCall = true;
   private _resolve: ((arg: any) => void) | undefined;
   private _reject: ((error: any) => void) | undefined;
   private _promise: Promise<any>;

packages/playwright-core/src/dispatchers/playwrightDispatcher.ts

@@ -29,7 +29,8 @@ import { ElectronDispatcher } from './electronDispatcher';
 import { APIRequestContextDispatcher } from './networkDispatchers';
 import { SelectorsDispatcher } from './selectorsDispatcher';
 
-export class PlaywrightDispatcher extends Dispatcher<Playwright, channels.PlaywrightInitializer, channels.PlaywrightEvents> implements channels.PlaywrightChannel {
+export class PlaywrightDispatcher extends Dispatcher<Playwright, channels.PlaywrightChannel> implements channels.PlaywrightChannel {
+  _type_Playwright;
   private _socksProxy: SocksProxy | undefined;
 
   constructor(scope: DispatcherScope, playwright: Playwright, customSelectors?: channels.SelectorsChannel, preLaunchedBrowser?: channels.BrowserChannel) {
@@ -46,6 +47,7 @@ export class PlaywrightDispatcher extends Dispatcher<Playwright, channels.Playwr
       selectors: customSelectors || new SelectorsDispatcher(scope, playwright.selectors),
       preLaunchedBrowser,
     }, false);
+    this._type_Playwright = true;
   }
 
   async enableSocksProxy() {

packages/playwright-core/src/dispatchers/selectorsDispatcher.ts

@@ -18,7 +18,8 @@ import { Dispatcher, DispatcherScope } from './dispatcher';
 import * as channels from '../protocol/channels';
 import { Selectors } from '../server/selectors';
 
-export class SelectorsDispatcher extends Dispatcher<Selectors, channels.SelectorsInitializer, channels.SelectorsEvents> implements channels.SelectorsChannel {
+export class SelectorsDispatcher extends Dispatcher<Selectors, channels.SelectorsChannel> implements channels.SelectorsChannel {
+  _type_Selectors = true;
   constructor(scope: DispatcherScope, selectors: Selectors) {
     super(scope, selectors, 'Selectors', {});
   }

packages/playwright-core/src/dispatchers/streamDispatcher.ts

@@ -19,7 +19,8 @@ import { Dispatcher, DispatcherScope } from './dispatcher';
 import * as stream from 'stream';
 import { createGuid } from '../utils/utils';
 
-export class StreamDispatcher extends Dispatcher<{ guid: string, stream: stream.Readable }, channels.StreamInitializer, channels.StreamEvents> implements channels.StreamChannel {
+export class StreamDispatcher extends Dispatcher<{ guid: string, stream: stream.Readable }, channels.StreamChannel> implements channels.StreamChannel {
+  _type_Stream = true;
   private _ended: boolean = false;
   constructor(scope: DispatcherScope, stream: stream.Readable) {
     super(scope, { guid: 'stream@' + createGuid(), stream }, 'Stream', {});

packages/playwright-core/src/protocol/channels.ts

@@ -16,13 +16,110 @@
 
 // This file is generated by generate_channels.js, do not edit manually.
 
-import { EventEmitter } from 'events';
-
 export type Binary = string;
 
-export interface Channel extends EventEmitter {
+export interface Channel {
 }
 
+// ----------- Initializer Traits -----------
+export type InitializerTraits<T> =
+    T extends JsonPipeChannel ? JsonPipeInitializer :
+    T extends AndroidDeviceChannel ? AndroidDeviceInitializer :
+    T extends AndroidSocketChannel ? AndroidSocketInitializer :
+    T extends AndroidChannel ? AndroidInitializer :
+    T extends ElectronApplicationChannel ? ElectronApplicationInitializer :
+    T extends ElectronChannel ? ElectronInitializer :
+    T extends CDPSessionChannel ? CDPSessionInitializer :
+    T extends StreamChannel ? StreamInitializer :
+    T extends ArtifactChannel ? ArtifactInitializer :
+    T extends DialogChannel ? DialogInitializer :
+    T extends BindingCallChannel ? BindingCallInitializer :
+    T extends ConsoleMessageChannel ? ConsoleMessageInitializer :
+    T extends WebSocketChannel ? WebSocketInitializer :
+    T extends ResponseChannel ? ResponseInitializer :
+    T extends RouteChannel ? RouteInitializer :
+    T extends RequestChannel ? RequestInitializer :
+    T extends ElementHandleChannel ? ElementHandleInitializer :
+    T extends JSHandleChannel ? JSHandleInitializer :
+    T extends WorkerChannel ? WorkerInitializer :
+    T extends FrameChannel ? FrameInitializer :
+    T extends PageChannel ? PageInitializer :
+    T extends BrowserContextChannel ? BrowserContextInitializer :
+    T extends EventTargetChannel ? EventTargetInitializer :
+    T extends BrowserChannel ? BrowserInitializer :
+    T extends BrowserTypeChannel ? BrowserTypeInitializer :
+    T extends SelectorsChannel ? SelectorsInitializer :
+    T extends PlaywrightChannel ? PlaywrightInitializer :
+    T extends RootChannel ? RootInitializer :
+    T extends APIRequestContextChannel ? APIRequestContextInitializer :
+    object;
+
+// ----------- Event Traits -----------
+export type EventsTraits<T> =
+    T extends JsonPipeChannel ? JsonPipeEvents :
+    T extends AndroidDeviceChannel ? AndroidDeviceEvents :
+    T extends AndroidSocketChannel ? AndroidSocketEvents :
+    T extends AndroidChannel ? AndroidEvents :
+    T extends ElectronApplicationChannel ? ElectronApplicationEvents :
+    T extends ElectronChannel ? ElectronEvents :
+    T extends CDPSessionChannel ? CDPSessionEvents :
+    T extends StreamChannel ? StreamEvents :
+    T extends ArtifactChannel ? ArtifactEvents :
+    T extends DialogChannel ? DialogEvents :
+    T extends BindingCallChannel ? BindingCallEvents :
+    T extends ConsoleMessageChannel ? ConsoleMessageEvents :
+    T extends WebSocketChannel ? WebSocketEvents :
+    T extends ResponseChannel ? ResponseEvents :
+    T extends RouteChannel ? RouteEvents :
+    T extends RequestChannel ? RequestEvents :
+    T extends ElementHandleChannel ? ElementHandleEvents :
+    T extends JSHandleChannel ? JSHandleEvents :
+    T extends WorkerChannel ? WorkerEvents :
+    T extends FrameChannel ? FrameEvents :
+    T extends PageChannel ? PageEvents :
+    T extends BrowserContextChannel ? BrowserContextEvents :
+    T extends EventTargetChannel ? EventTargetEvents :
+    T extends BrowserChannel ? BrowserEvents :
+    T extends BrowserTypeChannel ? BrowserTypeEvents :
+    T extends SelectorsChannel ? SelectorsEvents :
+    T extends PlaywrightChannel ? PlaywrightEvents :
+    T extends RootChannel ? RootEvents :
+    T extends APIRequestContextChannel ? APIRequestContextEvents :
+    undefined;
+
+// ----------- EventTarget Traits -----------
+export type EventTargetTraits<T> =
+    T extends JsonPipeChannel ? JsonPipeEventTarget :
+    T extends AndroidDeviceChannel ? AndroidDeviceEventTarget :
+    T extends AndroidSocketChannel ? AndroidSocketEventTarget :
+    T extends AndroidChannel ? AndroidEventTarget :
+    T extends ElectronApplicationChannel ? ElectronApplicationEventTarget :
+    T extends ElectronChannel ? ElectronEventTarget :
+    T extends CDPSessionChannel ? CDPSessionEventTarget :
+    T extends StreamChannel ? StreamEventTarget :
+    T extends ArtifactChannel ? ArtifactEventTarget :
+    T extends DialogChannel ? DialogEventTarget :
+    T extends BindingCallChannel ? BindingCallEventTarget :
+    T extends ConsoleMessageChannel ? ConsoleMessageEventTarget :
+    T extends WebSocketChannel ? WebSocketEventTarget :
+    T extends ResponseChannel ? ResponseEventTarget :
+    T extends RouteChannel ? RouteEventTarget :
+    T extends RequestChannel ? RequestEventTarget :
+    T extends ElementHandleChannel ? ElementHandleEventTarget :
+    T extends JSHandleChannel ? JSHandleEventTarget :
+    T extends WorkerChannel ? WorkerEventTarget :
+    T extends FrameChannel ? FrameEventTarget :
+    T extends PageChannel ? PageEventTarget :
+    T extends BrowserContextChannel ? BrowserContextEventTarget :
+    T extends EventTargetChannel ? EventTargetEventTarget :
+    T extends BrowserChannel ? BrowserEventTarget :
+    T extends BrowserTypeChannel ? BrowserTypeEventTarget :
+    T extends SelectorsChannel ? SelectorsEventTarget :
+    T extends PlaywrightChannel ? PlaywrightEventTarget :
+    T extends RootChannel ? RootEventTarget :
+    T extends APIRequestContextChannel ? APIRequestContextEventTarget :
+    undefined;
+
 export type StackFrame = {
   file: string,
   line?: number,
@@ -163,7 +260,10 @@ export type FormField = {
 
 // ----------- APIRequestContext -----------
 export type APIRequestContextInitializer = {};
-export interface APIRequestContextChannel extends Channel {
+export interface APIRequestContextEventTarget {
+}
+export interface APIRequestContextChannel extends APIRequestContextEventTarget, Channel {
+  _type_APIRequestContext: boolean;
   fetch(params: APIRequestContextFetchParams, metadata?: Metadata): Promise<APIRequestContextFetchResult>;
   fetchResponseBody(params: APIRequestContextFetchResponseBodyParams, metadata?: Metadata): Promise<APIRequestContextFetchResponseBodyResult>;
   storageState(params?: APIRequestContextStorageStateParams, metadata?: Metadata): Promise<APIRequestContextStorageStateResult>;
@@ -239,7 +339,10 @@ export type APIResponse = {
 export type LifecycleEvent = 'load' | 'domcontentloaded' | 'networkidle' | 'commit';
 // ----------- Root -----------
 export type RootInitializer = {};
-export interface RootChannel extends Channel {
+export interface RootEventTarget {
+}
+export interface RootChannel extends RootEventTarget, Channel {
+  _type_Root: boolean;
   initialize(params: RootInitializeParams, metadata?: Metadata): Promise<RootInitializeResult>;
 }
 export type RootInitializeParams = {
@@ -283,10 +386,13 @@ export type PlaywrightInitializer = {
   selectors: SelectorsChannel,
   preLaunchedBrowser?: BrowserChannel,
 };
-export interface PlaywrightChannel extends Channel {
+export interface PlaywrightEventTarget {
   on(event: 'socksRequested', callback: (params: PlaywrightSocksRequestedEvent) => void): this;
   on(event: 'socksData', callback: (params: PlaywrightSocksDataEvent) => void): this;
   on(event: 'socksClosed', callback: (params: PlaywrightSocksClosedEvent) => void): this;
+}
+export interface PlaywrightChannel extends PlaywrightEventTarget, Channel {
+  _type_Playwright: boolean;
   socksConnected(params: PlaywrightSocksConnectedParams, metadata?: Metadata): Promise<PlaywrightSocksConnectedResult>;
   socksFailed(params: PlaywrightSocksFailedParams, metadata?: Metadata): Promise<PlaywrightSocksFailedResult>;
   socksData(params: PlaywrightSocksDataParams, metadata?: Metadata): Promise<PlaywrightSocksDataResult>;
@@ -400,7 +506,10 @@ export interface PlaywrightEvents {
 
 // ----------- Selectors -----------
 export type SelectorsInitializer = {};
-export interface SelectorsChannel extends Channel {
+export interface SelectorsEventTarget {
+}
+export interface SelectorsChannel extends SelectorsEventTarget, Channel {
+  _type_Selectors: boolean;
   register(params: SelectorsRegisterParams, metadata?: Metadata): Promise<SelectorsRegisterResult>;
 }
 export type SelectorsRegisterParams = {
@@ -421,7 +530,10 @@ export type BrowserTypeInitializer = {
   executablePath: string,
   name: string,
 };
-export interface BrowserTypeChannel extends Channel {
+export interface BrowserTypeEventTarget {
+}
+export interface BrowserTypeChannel extends BrowserTypeEventTarget, Channel {
+  _type_BrowserType: boolean;
   connect(params: BrowserTypeConnectParams, metadata?: Metadata): Promise<BrowserTypeConnectResult>;
   launch(params: BrowserTypeLaunchParams, metadata?: Metadata): Promise<BrowserTypeLaunchResult>;
   launchPersistentContext(params: BrowserTypeLaunchPersistentContextParams, metadata?: Metadata): Promise<BrowserTypeLaunchPersistentContextResult>;
@@ -664,8 +776,11 @@ export type BrowserInitializer = {
   version: string,
   name: string,
 };
-export interface BrowserChannel extends Channel {
+export interface BrowserEventTarget {
   on(event: 'close', callback: (params: BrowserCloseEvent) => void): this;
+}
+export interface BrowserChannel extends BrowserEventTarget, Channel {
+  _type_Browser: boolean;
   close(params?: BrowserCloseParams, metadata?: Metadata): Promise<BrowserCloseResult>;
   killForTests(params?: BrowserKillForTestsParams, metadata?: Metadata): Promise<BrowserKillForTestsResult>;
   newContext(params: BrowserNewContextParams, metadata?: Metadata): Promise<BrowserNewContextResult>;
@@ -831,7 +946,10 @@ export interface BrowserEvents {
 
 // ----------- EventTarget -----------
 export type EventTargetInitializer = {};
-export interface EventTargetChannel extends Channel {
+export interface EventTargetEventTarget {
+}
+export interface EventTargetChannel extends EventTargetEventTarget, Channel {
+  _type_EventTarget: boolean;
   waitForEventInfo(params: EventTargetWaitForEventInfoParams, metadata?: Metadata): Promise<EventTargetWaitForEventInfoResult>;
 }
 export type EventTargetWaitForEventInfoParams = {
@@ -856,7 +974,7 @@ export type BrowserContextInitializer = {
   isChromium: boolean,
   APIRequestContext: APIRequestContextChannel,
 };
-export interface BrowserContextChannel extends EventTargetChannel {
+export interface BrowserContextEventTarget {
   on(event: 'bindingCall', callback: (params: BrowserContextBindingCallEvent) => void): this;
   on(event: 'close', callback: (params: BrowserContextCloseEvent) => void): this;
   on(event: 'page', callback: (params: BrowserContextPageEvent) => void): this;
@@ -868,6 +986,9 @@ export interface BrowserContextChannel extends EventTargetChannel {
   on(event: 'requestFailed', callback: (params: BrowserContextRequestFailedEvent) => void): this;
   on(event: 'requestFinished', callback: (params: BrowserContextRequestFinishedEvent) => void): this;
   on(event: 'response', callback: (params: BrowserContextResponseEvent) => void): this;
+}
+export interface BrowserContextChannel extends BrowserContextEventTarget, EventTargetChannel {
+  _type_BrowserContext: boolean;
   addCookies(params: BrowserContextAddCookiesParams, metadata?: Metadata): Promise<BrowserContextAddCookiesResult>;
   addInitScript(params: BrowserContextAddInitScriptParams, metadata?: Metadata): Promise<BrowserContextAddInitScriptResult>;
   clearCookies(params?: BrowserContextClearCookiesParams, metadata?: Metadata): Promise<BrowserContextClearCookiesResult>;
@@ -1153,7 +1274,7 @@ export type PageInitializer = {
   isClosed: boolean,
   opener?: PageChannel,
 };
-export interface PageChannel extends EventTargetChannel {
+export interface PageEventTarget {
   on(event: 'bindingCall', callback: (params: PageBindingCallEvent) => void): this;
   on(event: 'close', callback: (params: PageCloseEvent) => void): this;
   on(event: 'console', callback: (params: PageConsoleEvent) => void): this;
@@ -1170,6 +1291,9 @@ export interface PageChannel extends EventTargetChannel {
   on(event: 'video', callback: (params: PageVideoEvent) => void): this;
   on(event: 'webSocket', callback: (params: PageWebSocketEvent) => void): this;
   on(event: 'worker', callback: (params: PageWorkerEvent) => void): this;
+}
+export interface PageChannel extends PageEventTarget, EventTargetChannel {
+  _type_Page: boolean;
   setDefaultNavigationTimeoutNoReply(params: PageSetDefaultNavigationTimeoutNoReplyParams, metadata?: Metadata): Promise<PageSetDefaultNavigationTimeoutNoReplyResult>;
   setDefaultTimeoutNoReply(params: PageSetDefaultTimeoutNoReplyParams, metadata?: Metadata): Promise<PageSetDefaultTimeoutNoReplyResult>;
   setFileChooserInterceptedNoReply(params: PageSetFileChooserInterceptedNoReplyParams, metadata?: Metadata): Promise<PageSetFileChooserInterceptedNoReplyResult>;
@@ -1600,9 +1724,12 @@ export type FrameInitializer = {
   parentFrame?: FrameChannel,
   loadStates: LifecycleEvent[],
 };
-export interface FrameChannel extends Channel {
+export interface FrameEventTarget {
   on(event: 'loadstate', callback: (params: FrameLoadstateEvent) => void): this;
   on(event: 'navigated', callback: (params: FrameNavigatedEvent) => void): this;
+}
+export interface FrameChannel extends FrameEventTarget, Channel {
+  _type_Frame: boolean;
   evalOnSelector(params: FrameEvalOnSelectorParams, metadata?: Metadata): Promise<FrameEvalOnSelectorResult>;
   evalOnSelectorAll(params: FrameEvalOnSelectorAllParams, metadata?: Metadata): Promise<FrameEvalOnSelectorAllResult>;
   addScriptTag(params: FrameAddScriptTagParams, metadata?: Metadata): Promise<FrameAddScriptTagResult>;
@@ -2244,8 +2371,11 @@ export interface FrameEvents {
 export type WorkerInitializer = {
   url: string,
 };
-export interface WorkerChannel extends Channel {
+export interface WorkerEventTarget {
   on(event: 'close', callback: (params: WorkerCloseEvent) => void): this;
+}
+export interface WorkerChannel extends WorkerEventTarget, Channel {
+  _type_Worker: boolean;
   evaluateExpression(params: WorkerEvaluateExpressionParams, metadata?: Metadata): Promise<WorkerEvaluateExpressionResult>;
   evaluateExpressionHandle(params: WorkerEvaluateExpressionHandleParams, metadata?: Metadata): Promise<WorkerEvaluateExpressionHandleResult>;
 }
@@ -2281,8 +2411,11 @@ export interface WorkerEvents {
 export type JSHandleInitializer = {
   preview: string,
 };
-export interface JSHandleChannel extends Channel {
+export interface JSHandleEventTarget {
   on(event: 'previewUpdated', callback: (params: JSHandlePreviewUpdatedEvent) => void): this;
+}
+export interface JSHandleChannel extends JSHandleEventTarget, Channel {
+  _type_JSHandle: boolean;
   dispose(params?: JSHandleDisposeParams, metadata?: Metadata): Promise<JSHandleDisposeResult>;
   evaluateExpression(params: JSHandleEvaluateExpressionParams, metadata?: Metadata): Promise<JSHandleEvaluateExpressionResult>;
   evaluateExpressionHandle(params: JSHandleEvaluateExpressionHandleParams, metadata?: Metadata): Promise<JSHandleEvaluateExpressionHandleResult>;
@@ -2347,7 +2480,10 @@ export interface JSHandleEvents {
 
 // ----------- ElementHandle -----------
 export type ElementHandleInitializer = {};
-export interface ElementHandleChannel extends JSHandleChannel {
+export interface ElementHandleEventTarget {
+}
+export interface ElementHandleChannel extends ElementHandleEventTarget, JSHandleChannel {
+  _type_ElementHandle: boolean;
   evalOnSelector(params: ElementHandleEvalOnSelectorParams, metadata?: Metadata): Promise<ElementHandleEvalOnSelectorResult>;
   evalOnSelectorAll(params: ElementHandleEvalOnSelectorAllParams, metadata?: Metadata): Promise<ElementHandleEvalOnSelectorAllResult>;
   boundingBox(params?: ElementHandleBoundingBoxParams, metadata?: Metadata): Promise<ElementHandleBoundingBoxResult>;
@@ -2764,7 +2900,10 @@ export type RequestInitializer = {
   isNavigationRequest: boolean,
   redirectedFrom?: RequestChannel,
 };
-export interface RequestChannel extends Channel {
+export interface RequestEventTarget {
+}
+export interface RequestChannel extends RequestEventTarget, Channel {
+  _type_Request: boolean;
   response(params?: RequestResponseParams, metadata?: Metadata): Promise<RequestResponseResult>;
   rawRequestHeaders(params?: RequestRawRequestHeadersParams, metadata?: Metadata): Promise<RequestRawRequestHeadersResult>;
 }
@@ -2786,7 +2925,10 @@ export interface RequestEvents {
 export type RouteInitializer = {
   request: RequestChannel,
 };
-export interface RouteChannel extends Channel {
+export interface RouteEventTarget {
+}
+export interface RouteChannel extends RouteEventTarget, Channel {
+  _type_Route: boolean;
   abort(params: RouteAbortParams, metadata?: Metadata): Promise<RouteAbortResult>;
   continue(params: RouteContinueParams, metadata?: Metadata): Promise<RouteContinueResult>;
   fulfill(params: RouteFulfillParams, metadata?: Metadata): Promise<RouteFulfillResult>;
@@ -2850,7 +2992,10 @@ export type ResponseInitializer = {
   headers: NameValue[],
   timing: ResourceTiming,
 };
-export interface ResponseChannel extends Channel {
+export interface ResponseEventTarget {
+}
+export interface ResponseChannel extends ResponseEventTarget, Channel {
+  _type_Response: boolean;
   body(params?: ResponseBodyParams, metadata?: Metadata): Promise<ResponseBodyResult>;
   securityDetails(params?: ResponseSecurityDetailsParams, metadata?: Metadata): Promise<ResponseSecurityDetailsResult>;
   serverAddr(params?: ResponseServerAddrParams, metadata?: Metadata): Promise<ResponseServerAddrResult>;
@@ -2910,13 +3055,16 @@ export type RemoteAddr = {
 export type WebSocketInitializer = {
   url: string,
 };
-export interface WebSocketChannel extends EventTargetChannel {
+export interface WebSocketEventTarget {
   on(event: 'open', callback: (params: WebSocketOpenEvent) => void): this;
   on(event: 'frameSent', callback: (params: WebSocketFrameSentEvent) => void): this;
   on(event: 'frameReceived', callback: (params: WebSocketFrameReceivedEvent) => void): this;
   on(event: 'socketError', callback: (params: WebSocketSocketErrorEvent) => void): this;
   on(event: 'close', callback: (params: WebSocketCloseEvent) => void): this;
 }
+export interface WebSocketChannel extends WebSocketEventTarget, EventTargetChannel {
+  _type_WebSocket: boolean;
+}
 export type WebSocketOpenEvent = {};
 export type WebSocketFrameSentEvent = {
   opcode: number,
@@ -2950,7 +3098,10 @@ export type ConsoleMessageInitializer = {
     columnNumber: number,
   },
 };
-export interface ConsoleMessageChannel extends Channel {
+export interface ConsoleMessageEventTarget {
+}
+export interface ConsoleMessageChannel extends ConsoleMessageEventTarget, Channel {
+  _type_ConsoleMessage: boolean;
 }
 
 export interface ConsoleMessageEvents {
@@ -2963,7 +3114,10 @@ export type BindingCallInitializer = {
   args?: SerializedValue[],
   handle?: JSHandleChannel,
 };
-export interface BindingCallChannel extends Channel {
+export interface BindingCallEventTarget {
+}
+export interface BindingCallChannel extends BindingCallEventTarget, Channel {
+  _type_BindingCall: boolean;
   reject(params: BindingCallRejectParams, metadata?: Metadata): Promise<BindingCallRejectResult>;
   resolve(params: BindingCallResolveParams, metadata?: Metadata): Promise<BindingCallResolveResult>;
 }
@@ -2991,7 +3145,10 @@ export type DialogInitializer = {
   message: string,
   defaultValue: string,
 };
-export interface DialogChannel extends Channel {
+export interface DialogEventTarget {
+}
+export interface DialogChannel extends DialogEventTarget, Channel {
+  _type_Dialog: boolean;
   accept(params: DialogAcceptParams, metadata?: Metadata): Promise<DialogAcceptResult>;
   dismiss(params?: DialogDismissParams, metadata?: Metadata): Promise<DialogDismissResult>;
 }
@@ -3013,7 +3170,10 @@ export interface DialogEvents {
 export type ArtifactInitializer = {
   absolutePath: string,
 };
-export interface ArtifactChannel extends Channel {
+export interface ArtifactEventTarget {
+}
+export interface ArtifactChannel extends ArtifactEventTarget, Channel {
+  _type_Artifact: boolean;
   pathAfterFinished(params?: ArtifactPathAfterFinishedParams, metadata?: Metadata): Promise<ArtifactPathAfterFinishedResult>;
   saveAs(params: ArtifactSaveAsParams, metadata?: Metadata): Promise<ArtifactSaveAsResult>;
   saveAsStream(params?: ArtifactSaveAsStreamParams, metadata?: Metadata): Promise<ArtifactSaveAsStreamResult>;
@@ -3061,7 +3221,10 @@ export interface ArtifactEvents {
 
 // ----------- Stream -----------
 export type StreamInitializer = {};
-export interface StreamChannel extends Channel {
+export interface StreamEventTarget {
+}
+export interface StreamChannel extends StreamEventTarget, Channel {
+  _type_Stream: boolean;
   read(params: StreamReadParams, metadata?: Metadata): Promise<StreamReadResult>;
   close(params?: StreamCloseParams, metadata?: Metadata): Promise<StreamCloseResult>;
 }
@@ -3083,8 +3246,11 @@ export interface StreamEvents {
 
 // ----------- CDPSession -----------
 export type CDPSessionInitializer = {};
-export interface CDPSessionChannel extends Channel {
+export interface CDPSessionEventTarget {
   on(event: 'event', callback: (params: CDPSessionEventEvent) => void): this;
+}
+export interface CDPSessionChannel extends CDPSessionEventTarget, Channel {
+  _type_CDPSession: boolean;
   send(params: CDPSessionSendParams, metadata?: Metadata): Promise<CDPSessionSendResult>;
   detach(params?: CDPSessionDetachParams, metadata?: Metadata): Promise<CDPSessionDetachResult>;
 }
@@ -3112,7 +3278,10 @@ export interface CDPSessionEvents {
 
 // ----------- Electron -----------
 export type ElectronInitializer = {};
-export interface ElectronChannel extends Channel {
+export interface ElectronEventTarget {
+}
+export interface ElectronChannel extends ElectronEventTarget, Channel {
+  _type_Electron: boolean;
   launch(params: ElectronLaunchParams, metadata?: Metadata): Promise<ElectronLaunchResult>;
 }
 export type ElectronLaunchParams = {
@@ -3198,8 +3367,11 @@ export interface ElectronEvents {
 export type ElectronApplicationInitializer = {
   context: BrowserContextChannel,
 };
-export interface ElectronApplicationChannel extends EventTargetChannel {
+export interface ElectronApplicationEventTarget {
   on(event: 'close', callback: (params: ElectronApplicationCloseEvent) => void): this;
+}
+export interface ElectronApplicationChannel extends ElectronApplicationEventTarget, EventTargetChannel {
+  _type_ElectronApplication: boolean;
   browserWindow(params: ElectronApplicationBrowserWindowParams, metadata?: Metadata): Promise<ElectronApplicationBrowserWindowResult>;
   evaluateExpression(params: ElectronApplicationEvaluateExpressionParams, metadata?: Metadata): Promise<ElectronApplicationEvaluateExpressionResult>;
   evaluateExpressionHandle(params: ElectronApplicationEvaluateExpressionHandleParams, metadata?: Metadata): Promise<ElectronApplicationEvaluateExpressionHandleResult>;
@@ -3247,7 +3419,10 @@ export interface ElectronApplicationEvents {
 
 // ----------- Android -----------
 export type AndroidInitializer = {};
-export interface AndroidChannel extends Channel {
+export interface AndroidEventTarget {
+}
+export interface AndroidChannel extends AndroidEventTarget, Channel {
+  _type_Android: boolean;
   devices(params?: AndroidDevicesParams, metadata?: Metadata): Promise<AndroidDevicesResult>;
   setDefaultTimeoutNoReply(params: AndroidSetDefaultTimeoutNoReplyParams, metadata?: Metadata): Promise<AndroidSetDefaultTimeoutNoReplyResult>;
 }
@@ -3269,9 +3444,12 @@ export interface AndroidEvents {
 
 // ----------- AndroidSocket -----------
 export type AndroidSocketInitializer = {};
-export interface AndroidSocketChannel extends Channel {
+export interface AndroidSocketEventTarget {
   on(event: 'data', callback: (params: AndroidSocketDataEvent) => void): this;
   on(event: 'close', callback: (params: AndroidSocketCloseEvent) => void): this;
+}
+export interface AndroidSocketChannel extends AndroidSocketEventTarget, Channel {
+  _type_AndroidSocket: boolean;
   write(params: AndroidSocketWriteParams, metadata?: Metadata): Promise<AndroidSocketWriteResult>;
   close(params?: AndroidSocketCloseParams, metadata?: Metadata): Promise<AndroidSocketCloseResult>;
 }
@@ -3300,9 +3478,12 @@ export type AndroidDeviceInitializer = {
   model: string,
   serial: string,
 };
-export interface AndroidDeviceChannel extends EventTargetChannel {
+export interface AndroidDeviceEventTarget {
   on(event: 'webViewAdded', callback: (params: AndroidDeviceWebViewAddedEvent) => void): this;
   on(event: 'webViewRemoved', callback: (params: AndroidDeviceWebViewRemovedEvent) => void): this;
+}
+export interface AndroidDeviceChannel extends AndroidDeviceEventTarget, EventTargetChannel {
+  _type_AndroidDevice: boolean;
   wait(params: AndroidDeviceWaitParams, metadata?: Metadata): Promise<AndroidDeviceWaitResult>;
   fill(params: AndroidDeviceFillParams, metadata?: Metadata): Promise<AndroidDeviceFillResult>;
   tap(params: AndroidDeviceTapParams, metadata?: Metadata): Promise<AndroidDeviceTapResult>;
@@ -3698,9 +3879,12 @@ export type AndroidElementInfo = {
 
 // ----------- JsonPipe -----------
 export type JsonPipeInitializer = {};
-export interface JsonPipeChannel extends Channel {
+export interface JsonPipeEventTarget {
   on(event: 'message', callback: (params: JsonPipeMessageEvent) => void): this;
   on(event: 'closed', callback: (params: JsonPipeClosedEvent) => void): this;
+}
+export interface JsonPipeChannel extends JsonPipeEventTarget, Channel {
+  _type_JsonPipe: boolean;
   send(params: JsonPipeSendParams, metadata?: Metadata): Promise<JsonPipeSendResult>;
   close(params?: JsonPipeCloseParams, metadata?: Metadata): Promise<JsonPipeCloseResult>;
 }

utils/generate_channels.js

@@ -124,11 +124,9 @@ const channels_ts = [
 
 // This file is generated by ${path.basename(__filename).split(path.sep).join(path.posix.sep)}, do not edit manually.
 
-import { EventEmitter } from 'events';
-
 export type Binary = string;
 
-export interface Channel extends EventEmitter {
+export interface Channel {
 }
 `];
 
@@ -202,6 +200,35 @@ for (const [name, item] of Object.entries(protocol)) {
   }
 }
 
+channels_ts.push(`// ----------- Initializer Traits -----------`);
+channels_ts.push(`export type InitializerTraits<T> =`);
+const entriesInReverse = Object.entries(protocol).reverse();
+for (const [name, item] of entriesInReverse) {
+  if (item.type !== 'interface')
+    continue;
+  channels_ts.push(`    T extends ${name}Channel ? ${name}Initializer :`);
+}
+channels_ts.push(`    object;`);
+channels_ts.push(``);
+channels_ts.push(`// ----------- Event Traits -----------`);
+channels_ts.push(`export type EventsTraits<T> =`);
+for (const [name, item] of entriesInReverse) {
+  if (item.type !== 'interface')
+    continue;
+  channels_ts.push(`    T extends ${name}Channel ? ${name}Events :`);
+}
+channels_ts.push(`    undefined;`);
+channels_ts.push(``);
+channels_ts.push(`// ----------- EventTarget Traits -----------`);
+channels_ts.push(`export type EventTargetTraits<T> =`);
+for (const [name, item] of entriesInReverse) {
+  if (item.type !== 'interface')
+    continue;
+  channels_ts.push(`    T extends ${name}Channel ? ${name}EventTarget :`);
+}
+channels_ts.push(`    undefined;`);
+channels_ts.push(``);
+
 for (const [name, item] of Object.entries(protocol)) {
   if (item.type === 'interface') {
     const channelName = name;
@@ -210,7 +237,7 @@ for (const [name, item] of Object.entries(protocol)) {
     const initializerName = channelName + 'Initializer';
     channels_ts.push(`export type ${initializerName} = ${init.ts};`);
 
-    channels_ts.push(`export interface ${channelName}Channel extends ${(item.extends || '') + 'Channel'} {`);
+    channels_ts.push(`export interface ${channelName}EventTarget {`);
     const ts_types = new Map();
 
     /** @type{{eventName: string, eventType: string}[]} */
@@ -224,7 +251,10 @@ for (const [name, item] of Object.entries(protocol)) {
       channels_ts.push(`  on(event: '${eventName}', callback: (params: ${paramsName}) => void): this;`);
       eventTypes.push({eventName, eventType: paramsName});
     }
+    channels_ts.push(`}`);
 
+    channels_ts.push(`export interface ${channelName}Channel extends ${channelName}EventTarget, ${(item.extends || '') + 'Channel'} {`);
+    channels_ts.push(`  _type_${channelName}: boolean;`);
     for (let [methodName, method] of Object.entries(item.commands || {})) {
       if (method === null)
         method = {};