fix(focus-monitor): implement OnDestroy logic (#9305)

Similarly to most of the other DOM-related services, these changes implement `ngOnDestroy` for the `FocusMonitor` which removes the monitoring from all of the currently-monitored elements.

Author: crisbeto

src/cdk/a11y/focus-monitor.spec.ts

@@ -186,14 +186,28 @@ describe('FocusMonitor', () => {
     fixture.detectChanges();
     tick();
 
-    expect(buttonElement.classList.length)
-        .toBe(2, 'button should have exactly 2 focus classes');
+    expect(buttonElement.classList.length).toBe(2, 'button should have exactly 2 focus classes');
 
     focusMonitor.stopMonitoring(buttonElement);
     fixture.detectChanges();
 
     expect(buttonElement.classList.length).toBe(0, 'button should not have any focus classes');
   }));
+
+  it('should remove classes when destroyed', fakeAsync(() => {
+    buttonElement.focus();
+    fixture.detectChanges();
+    tick();
+
+    expect(buttonElement.classList.length).toBe(2, 'button should have exactly 2 focus classes');
+
+    // Destroy manually since destroying the fixture won't do it.
+    focusMonitor.ngOnDestroy();
+    fixture.detectChanges();
+
+    expect(buttonElement.classList.length).toBe(0, 'button should not have any focus classes');
+  }));
+
 });
 
 

src/cdk/a11y/focus-monitor.ts

@@ -42,7 +42,7 @@ type MonitoredElementInfo = {
 
 /** Monitors mouse and keyboard events to determine the cause of focus events. */
 @Injectable()
-export class FocusMonitor {
+export class FocusMonitor implements OnDestroy {
   /** The focus origin that the next focus event is a result of. */
   private _origin: FocusOrigin = null;
 
@@ -58,8 +58,8 @@ export class FocusMonitor {
   /** The timeout id of the touch timeout, used to cancel timeout later. */
   private _touchTimeout: number;
 
-  /** Weak map of elements being monitored to their info. */
-  private _elementInfo = new WeakMap<Element, MonitoredElementInfo>();
+  /** Map of elements being monitored to their info. */
+  private _elementInfo = new Map<HTMLElement, MonitoredElementInfo>();
 
   /** A map of global objects to lists of current listeners. */
   private _unregisterGlobalListeners = () => {};
@@ -135,7 +135,7 @@ export class FocusMonitor {
    * @param element The element to stop monitoring.
    */
   stopMonitoring(element: HTMLElement): void {
-    let elementInfo = this._elementInfo.get(element);
+    const elementInfo = this._elementInfo.get(element);
 
     if (elementInfo) {
       elementInfo.unlisten();
@@ -157,6 +157,10 @@ export class FocusMonitor {
     element.focus();
   }
 
+  ngOnDestroy() {
+    this._elementInfo.forEach((_info, element) => this.stopMonitoring(element));
+  }
+
   /** Register necessary event listeners on the document and window. */
   private _registerGlobalListeners() {
     // Do nothing if we're not on the browser platform.