chore(waitForEvent): refactor waitForEvent into a single implementation (#1602)

Moves the `waitForEvent` implementation into an `ExtendedEventEmitter` class.

This is step one if we want to add `waitForEvent` to `Worker`, `Browser`, and `BrowserServer` objects. All of these only have a 'close' event, but I still feel we should be consistent with our event emitters.

src/browserContext.ts

@@ -18,10 +18,10 @@
 import { helper } from './helper';
 import * as network from './network';
 import { Page, PageBinding } from './page';
-import * as platform from './platform';
 import { TimeoutSettings } from './timeoutSettings';
 import * as types from './types';
 import { Events } from './events';
+import { ExtendedEventEmitter } from './extendedEventEmitter';
 
 export type BrowserContextOptions = {
   viewport?: types.Size | null,
@@ -62,7 +62,7 @@ export interface BrowserContext {
   close(): Promise<void>;
 }
 
-export abstract class BrowserContextBase extends platform.EventEmitter implements BrowserContext {
+export abstract class BrowserContextBase extends ExtendedEventEmitter implements BrowserContext {
   readonly _timeoutSettings = new TimeoutSettings();
   readonly _pageBindings = new Map<string, PageBinding>();
   readonly _options: BrowserContextOptions;
@@ -78,6 +78,14 @@ export abstract class BrowserContextBase extends platform.EventEmitter implement
     this._closePromise = new Promise(fulfill => this._closePromiseFulfill = fulfill);
   }
 
+  protected _abortPromiseForEvent(event: string) {
+    return event === Events.BrowserContext.Close ? super._abortPromiseForEvent(event) : this._closePromise;
+  }
+
+  protected _timeoutForEvent(event: string): number {
+    return this._timeoutSettings.timeout();
+  }
+
   _browserClosed() {
     for (const page of this.pages())
       page._didClose();
@@ -132,17 +140,6 @@ export abstract class BrowserContextBase extends platform.EventEmitter implement
   setDefaultTimeout(timeout: number) {
     this._timeoutSettings.setDefaultTimeout(timeout);
   }
-
-  async waitForEvent(event: string, optionsOrPredicate?: Function | (types.TimeoutOptions & { predicate?: Function })): Promise<any> {
-    if (!optionsOrPredicate)
-      optionsOrPredicate = {};
-    if (typeof optionsOrPredicate === 'function')
-      optionsOrPredicate = { predicate: optionsOrPredicate };
-    const { timeout = this._timeoutSettings.timeout(), predicate = () => true } = optionsOrPredicate;
-
-    const abortPromise = (event === Events.BrowserContext.Close) ? new Promise<Error>(() => { }) : this._closePromise;
-    return helper.waitForEvent(this, event, (...args: any[]) => !!predicate(...args), timeout, abortPromise);
-  }
 }
 
 export function assertBrowserContextIsNotOwned(context: BrowserContextBase) {

src/extendedEventEmitter.ts

@@ -0,0 +1,36 @@
+/**
+ * Copyright (c) Microsoft Corporation.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import { EventEmitter } from './platform';
+import { helper } from './helper';
+
+export class ExtendedEventEmitter extends EventEmitter {
+  protected _abortPromiseForEvent(event: string) {
+    return new Promise<Error>(() => void 0);
+  }
+
+  protected _timeoutForEvent(event: string): number {
+    throw new Error('unimplemented');
+  }
+
+  async waitForEvent(event: string, optionsOrPredicate: Function|{ predicate?: Function, timeout?: number } = {}): Promise<any> {
+    const {
+      predicate = () => true,
+      timeout = this._timeoutForEvent(event)
+    } = typeof optionsOrPredicate === 'function' ? {predicate: optionsOrPredicate} : optionsOrPredicate;
+    return helper.waitForEvent(this, event, predicate, timeout, this._abortPromiseForEvent(event));
+  }
+}

src/page.ts

@@ -29,6 +29,7 @@ import { BrowserContext, BrowserContextBase } from './browserContext';
 import { ConsoleMessage, ConsoleMessageLocation } from './console';
 import * as accessibility from './accessibility';
 import * as platform from './platform';
+import { ExtendedEventEmitter } from './extendedEventEmitter';
 
 export interface PageDelegate {
   readonly rawMouse: input.RawMouse;
@@ -87,7 +88,7 @@ export type FileChooser = {
   multiple: boolean
 };
 
-export class Page extends platform.EventEmitter {
+export class Page extends ExtendedEventEmitter {
   private _closed = false;
   private _closedCallback: () => void;
   private _closedPromise: Promise<void>;
@@ -142,6 +143,14 @@ export class Page extends platform.EventEmitter {
     this.coverage = delegate.coverage ? delegate.coverage() : null;
   }
 
+  protected _abortPromiseForEvent(event: string) {
+    return this._disconnectedPromise;
+  }
+
+  protected _timeoutForEvent(event: string): number {
+    return this._timeoutSettings.timeout();
+  }
+
   _didClose() {
     assert(!this._closed, 'Page closed twice');
     this._closed = true;
@@ -303,13 +312,6 @@ export class Page extends platform.EventEmitter {
     return this.mainFrame().waitForNavigation(options);
   }
 
-  async waitForEvent(event: string, optionsOrPredicate: Function | (types.TimeoutOptions & { predicate?: Function }) = {}): Promise<any> {
-    if (typeof optionsOrPredicate === 'function')
-      optionsOrPredicate = { predicate: optionsOrPredicate };
-    const { timeout = this._timeoutSettings.timeout(), predicate = () => true } = optionsOrPredicate;
-    return helper.waitForEvent(this, event, (...args: any[]) => !!predicate(...args), timeout, this._disconnectedPromise);
-  }
-
   async waitForRequest(urlOrPredicate: string | RegExp | ((r: network.Request) => boolean), options: types.TimeoutOptions = {}): Promise<network.Request> {
     const { timeout = this._timeoutSettings.timeout() } = options;
     return helper.waitForEvent(this, Events.Page.Request, (request: network.Request) => {