feat(a11y): add injection token configure default politeness and duration

Adds an injection token that allows consumers to configure the default `politeness` and `duration` for the live announcer.

Fixes #15121.

Author: crisbeto

src/cdk/a11y/live-announcer/live-announcer-token.ts

@@ -0,0 +1,39 @@
+/**
+ * @license
+ * Copyright Google LLC All Rights Reserved.
+ *
+ * Use of this source code is governed by an MIT-style license that can be
+ * found in the LICENSE file at https://angular.io/license
+ */
+
+import {InjectionToken} from '@angular/core';
+
+// The tokens for the live announcer are defined in a separate file from LiveAnnouncer
+// as a workaround for https://github.com/angular/angular/issues/22559
+
+/** Possible politeness levels. */
+export type AriaLivePoliteness = 'off' | 'polite' | 'assertive';
+
+export const LIVE_ANNOUNCER_ELEMENT_TOKEN =
+    new InjectionToken<HTMLElement | null>('liveAnnouncerElement', {
+      providedIn: 'root',
+      factory: LIVE_ANNOUNCER_ELEMENT_TOKEN_FACTORY,
+    });
+
+/** @docs-private */
+export function LIVE_ANNOUNCER_ELEMENT_TOKEN_FACTORY(): null {
+  return null;
+}
+
+/** Object that can be used to configure the default options for the LiveAnnouncer. */
+export interface LiveAnnouncerDefaultOptions {
+  /** Default politeness for the announcements. */
+  politeness?: AriaLivePoliteness;
+
+  /** Default duration for the announcement messages. */
+  duration?: number;
+}
+
+/** Injection token that can be used to configure the default options for the LiveAnnouncer. */
+export const LIVE_ANNOUNCER_DEFAULT_OPTIONS =
+    new InjectionToken<LiveAnnouncerDefaultOptions>('LIVE_ANNOUNCER_DEFAULT_OPTIONS');

src/cdk/a11y/live-announcer/live-announcer-tokens.ts

@@ -4,7 +4,11 @@ import {ComponentFixture, fakeAsync, flush, inject, TestBed, tick} from '@angula
 import {By} from '@angular/platform-browser';
 import {A11yModule} from '../index';
 import {LiveAnnouncer} from './live-announcer';
-import {LIVE_ANNOUNCER_ELEMENT_TOKEN} from './live-announcer-token';
+import {
+  LIVE_ANNOUNCER_ELEMENT_TOKEN,
+  LIVE_ANNOUNCER_DEFAULT_OPTIONS,
+  LiveAnnouncerDefaultOptions,
+} from './live-announcer-tokens';
 
 
 describe('LiveAnnouncer', () => {
@@ -189,6 +193,47 @@ describe('LiveAnnouncer', () => {
       expect(customLiveElement.textContent).toBe('Custom Element');
     }));
   });
+
+  describe('with a default options', () => {
+    beforeEach(() => {
+      return TestBed.configureTestingModule({
+        imports: [A11yModule],
+        declarations: [TestApp],
+        providers: [{
+          provide: LIVE_ANNOUNCER_DEFAULT_OPTIONS,
+          useValue: {
+            politeness: 'assertive',
+            duration: 1337
+          } as LiveAnnouncerDefaultOptions
+        }],
+      });
+    });
+
+    beforeEach(inject([LiveAnnouncer], (la: LiveAnnouncer) => {
+      announcer = la;
+      ariaLiveElement = getLiveElement();
+    }));
+
+    it('should pick up the default politeness from the injection token', fakeAsync(() => {
+      announcer.announce('Hello');
+
+      tick(2000);
+
+      expect(ariaLiveElement.getAttribute('aria-live')).toBe('assertive');
+    }));
+
+    it('should pick up the default politeness from the injection token', fakeAsync(() => {
+      announcer.announce('Hello');
+
+      tick(100);
+      expect(ariaLiveElement.textContent).toBe('Hello');
+
+      tick(1337);
+      expect(ariaLiveElement.textContent).toBeFalsy();
+    }));
+
+  });
+
 });
 
 describe('CdkAriaLive', () => {

src/cdk/a11y/live-announcer/live-announcer.spec.ts

@@ -21,11 +21,13 @@ import {
   SkipSelf,
 } from '@angular/core';
 import {Subscription} from 'rxjs';
-import {LIVE_ANNOUNCER_ELEMENT_TOKEN} from './live-announcer-token';
-
+import {
+  AriaLivePoliteness,
+  LiveAnnouncerDefaultOptions,
+  LIVE_ANNOUNCER_ELEMENT_TOKEN,
+  LIVE_ANNOUNCER_DEFAULT_OPTIONS,
+} from './live-announcer-tokens';
 
-/** Possible politeness levels. */
-export type AriaLivePoliteness = 'off' | 'polite' | 'assertive';
 
 @Injectable({providedIn: 'root'})
 export class LiveAnnouncer implements OnDestroy {
@@ -36,7 +38,9 @@ export class LiveAnnouncer implements OnDestroy {
   constructor(
       @Optional() @Inject(LIVE_ANNOUNCER_ELEMENT_TOKEN) elementToken: any,
       private _ngZone: NgZone,
-      @Inject(DOCUMENT) _document: any) {
+      @Inject(DOCUMENT) _document: any,
+      @Optional() @Inject(LIVE_ANNOUNCER_DEFAULT_OPTIONS)
+          private _defaultOptions?: LiveAnnouncerDefaultOptions) {
 
     // We inject the live element and document as `any` because the constructor signature cannot
     // reference browser globals (HTMLElement, Document) on non-browser environments, since having
@@ -82,8 +86,9 @@ export class LiveAnnouncer implements OnDestroy {
   announce(message: string, politeness?: AriaLivePoliteness, duration?: number): Promise<void>;
 
   announce(message: string, ...args: any[]): Promise<void> {
-    let politeness: AriaLivePoliteness;
-    let duration: number;
+    const defaultOptions = this._defaultOptions;
+    let politeness: AriaLivePoliteness | undefined;
+    let duration: number | undefined;
 
     if (args.length === 1 && typeof args[0] === 'number') {
       duration = args[0];
@@ -94,8 +99,17 @@ export class LiveAnnouncer implements OnDestroy {
     this.clear();
     clearTimeout(this._previousTimeout);
 
+    if (!politeness) {
+      politeness =
+          (defaultOptions && defaultOptions.politeness) ? defaultOptions.politeness : 'polite';
+    }
+
+    if (duration == null && defaultOptions) {
+      duration = defaultOptions.duration;
+    }
+
     // TODO: ensure changing the politeness works on all environments we support.
-    this._liveElement.setAttribute('aria-live', politeness! || 'polite');
+    this._liveElement.setAttribute('aria-live', politeness);
 
     // This 100ms timeout is necessary for some browser + screen-reader combinations:
     // - Both JAWS and NVDA over IE11 will not announce anything without a non-zero timeout.

src/cdk/a11y/live-announcer/live-announcer.ts

@@ -12,7 +12,7 @@ export * from './key-manager/list-key-manager';
 export * from './focus-trap/focus-trap';
 export * from './interactivity-checker/interactivity-checker';
 export * from './live-announcer/live-announcer';
-export * from './live-announcer/live-announcer-token';
+export * from './live-announcer/live-announcer-tokens';
 export * from './focus-monitor/focus-monitor';
 export * from './fake-mousedown';
 export * from './a11y-module';