Class ImagePerformanceWarning

packages/core/src/image_performance_warning.ts:26–205

@Service()
export class ImagePerformanceWarning implements OnDestroy {
  // Map of full image URLs -> original `ngSrc` values.
  private window: Window | null = null;
  private observer: PerformanceObserver | null = null;
  private options: ImageConfig = inject(IMAGE_CONFIG);
  private lcpImageUrl?: string;

  public start() {
    if (
      (typeof ngServerMode !== 'undefined' && ngServerMode) ||
      typeof PerformanceObserver === 'undefined' ||
      (this.options?.disableImageSizeWarning && this.options?.disableImageLazyLoadWarning)
    ) {
      return;
    }
    this.observer = this.initPerformanceObserver();
    const doc = getDocument();
    const win = doc.defaultView;
    if (win) {
      this.window = win;
      // Wait to avoid race conditions where LCP image triggers
      // load event before it's recorded by the performance observer
      const waitToScan = () => {
        setTimeout(this.scanImages.bind(this), SCAN_DELAY);
      };
      const setup = () => {
        // Consider the case when the application is created and destroyed multiple times.
        // Typically, applications are created instantly once the page is loaded, and the
        // `window.load` listener is always triggered. However, the `window.load` event will never
        // be fired if the page is loaded, and the application is created later. Checking for
        // `readyState` is the easiest way to determine whether the page has been loaded or not.
        if (doc.readyState === 'complete') {
          waitToScan();
        } else {
          this.window?.addEventListener('load', waitToScan, {once: true});
        }
      };
      // Angular doesn't have to run change detection whenever any asynchronous tasks are invoked in
      // the scope of this functionality.
      if (typeof Zone !== 'undefined') {
        Zone.root.run(() => setup());
      } else {
        setup();
      }
    }
  }

  ngOnDestroy() {
    this.observer?.disconnect();
  }

  private initPerformanceObserver(): PerformanceObserver | null {
    if (typeof PerformanceObserver === 'undefined') {
      return null;
    }
    const observer = new PerformanceObserver((entryList) => {
      const entries = entryList.getEntries();
      if (entries.length === 0) return;