Method constructor

src/utils/display-observer.js:106–158

* @param {!AmpDoc} ampdoc

(ampdoc)

   * @param {!AmpDoc} ampdoc
   */
  constructor(ampdoc) {
    /** @private @const */
    this.ampdoc_ = ampdoc;

    const {win} = ampdoc;
    const body = ampdoc.getBody();

    this.observed_ = this.observed_.bind(this);
    this.containerObserved_ = this.containerObserved_.bind(this);

    /** @private @const {!Array<!ObserverDef>} */
    this.observers_ = [];

    // Viewport observer is only needed because `position:fixed` elements
    // are not observable by a documentElement or body's root.
    this.observers_.push({
      container: null,
      root: null,
      contains: () => true,
      io: new win.IntersectionObserver(this.observed_, {
        threshold: DISPLAY_THRESHOLD,
      }),
    });

    // Body observer: very close to `display:none` observer.
    this.observers_.push({
      container: body,
      root: body,
      contains: () => true,
      io: new win.IntersectionObserver(this.observed_, {
        root: body,
        threshold: DISPLAY_THRESHOLD,
      }),
    });

    /** @private {boolean} */
    this.isDocDisplay_ = computeDocIsDisplayed(ampdoc.getVisibilityState());

    /** @private {?UnlistenDef} */
    this.visibilityUnlisten_ = ampdoc.onVisibilityChanged(() => {
      const display = computeDocIsDisplayed(ampdoc.getVisibilityState());
      if (display !== this.isDocDisplay_) {
        this.isDocDisplay_ = display;
        this.docVisibilityChanged_();
      }
    });

    /** @private @const {!Map<!Element, !Array<!ObserverCallbackDef>>} */
    this.targetObserverCallbacks_ = new Map();

    /** @private @const {!Map<!Element, !Array<boolean>>} */
    this.targetObservations_ = new Map();
  }

  /** @override */
  dispose() {