refactor(youtube-player): fix strict property initialization errors

Updates the code to be compatible with strict property initialization.

Author: crisbeto

src/youtube-player/tsconfig.json

@@ -5,7 +5,8 @@
     "rootDir": "..",
     "baseUrl": ".",
     "paths": {},
-    "types": ["jasmine"]
+    "types": ["jasmine"],
+    "strictPropertyInitialization": true
   },
   "include": ["*.ts", "../dev-mode-types.d.ts"]
 }

src/youtube-player/youtube-player-placeholder.ts

@@ -39,22 +39,22 @@ export type PlaceholderImageQuality = 'high' | 'standard' | 'low';
 })
 export class YouTubePlayerPlaceholder {
   /** ID of the video for which to show the placeholder. */
-  @Input() videoId: string;
+  @Input() videoId!: string;
 
   /** Width of the video for which to show the placeholder. */
-  @Input() width: number;
+  @Input() width!: number;
 
   /** Height of the video for which to show the placeholder. */
-  @Input() height: number;
+  @Input() height!: number;
 
   /** Whether the video is currently being loaded. */
-  @Input() isLoading: boolean;
+  @Input() isLoading: boolean = false;
 
   /** Accessible label for the play button. */
-  @Input() buttonLabel: string;
+  @Input() buttonLabel!: string;
 
   /** Quality of the placeholder image. */
-  @Input() quality: PlaceholderImageQuality;
+  @Input() quality!: PlaceholderImageQuality;
 
   /** Gets the background image showing the placeholder. */
   protected _getBackgroundImage(): string | undefined {

src/youtube-player/youtube-player.spec.ts

@@ -803,7 +803,7 @@ class TestApp {
   onPlaybackRateChange = jasmine.createSpy('onPlaybackRateChange');
   onError = jasmine.createSpy('onError');
   onApiChange = jasmine.createSpy('onApiChange');
-  @ViewChild('player') youtubePlayer: YouTubePlayer;
+  @ViewChild('player') youtubePlayer!: YouTubePlayer;
 }
 
 @Component({
@@ -821,6 +821,6 @@ class StaticStartEndSecondsApp {
   template: `<youtube-player [videoId]="videoId"/>`,
 })
 class NoEventsApp {
-  @ViewChild(YouTubePlayer) player: YouTubePlayer;
+  @ViewChild(YouTubePlayer) player!: YouTubePlayer;
   videoId = VIDEO_ID;
 }

src/youtube-player/youtube-player.ts

@@ -251,7 +251,7 @@ export class YouTubePlayer implements AfterViewInit, OnChanges, OnDestroy {
 
   /** The element that will be replaced by the iframe. */
   @ViewChild('youtubeContainer', {static: true})
-  youtubeContainer: ElementRef<HTMLElement>;
+  youtubeContainer!: ElementRef<HTMLElement>;
 
   constructor(...args: unknown[]);