Function loadPromise

src/utils/event-helper.js:156–215

(eleOrWindow)

 * @template T
 */
export function loadPromise(eleOrWindow) {
  let unlistenLoad;
  let unlistenError;
  if (isLoaded(eleOrWindow)) {
    return Promise.resolve(eleOrWindow);
  }
  const isMediaElement = isHTMLMediaElement(eleOrWindow);
  if (
    isMediaElement &&
    eleOrWindow[MEDIA_LOAD_FAILURE_SRC_PROPERTY] === eleOrWindow.currentSrc
  ) {
    return Promise.reject(eleOrWindow);
  }
  const loadingPromise = new Promise((resolve, reject) => {
    // Listen once since IE 5/6/7 fire the onload event continuously for
    // animated GIFs.
    if (isMediaElement) {
      // The following event can be triggered by the media or one of its
      // sources. Using capture is required as the media events do not bubble.
      unlistenLoad = listenOnce(eleOrWindow, 'loadedmetadata', resolve, {
        capture: true,
      });
    } else {
      unlistenLoad = listenOnce(eleOrWindow, 'load', resolve);
    }
    // Don't unlisten on error for Windows.
    if (!eleOrWindow.tagName) {
      return;
    }
    let errorTarget = eleOrWindow;
    // If the media element has no `src`, it will try to load the sources in
    // document order. If the last source errors, then the media element
    // loading errored.
    if (isMediaElement && !eleOrWindow.hasAttribute('src')) {
      errorTarget = lastChildElement(
        eleOrWindow,
        (child) => child.tagName === 'SOURCE'
      );
      if (!errorTarget) {
        return reject(new Error('Media has no source.'));
      }
    }
    unlistenError = listenOnce(errorTarget, 'error', reject);
  });

  return loadingPromise.then(
    () => {
      if (unlistenError) {
        unlistenError();
      }
      return eleOrWindow;
    },
    () => {
      if (unlistenLoad) {
        unlistenLoad();
      }
      failedToLoad(eleOrWindow);
    }