Method layoutCallback

src/custom-element.js:1623–1681

* Instructs the element to layout its content and load its resources if * necessary by calling the BaseElement.layoutCallback method that * should be implemented by BaseElement subclasses. Must return a promise * that will yield when the layout and associated loadings are comp

(signal)

     * TODO(#31915): remove once R1 migration is complete.
     */
    layoutCallback(signal) {
      assertNotTemplate(this);
      devAssert(this.isBuilt(), 'Must be built to receive viewport events');
      // A lot of tests call layoutCallback manually, and don't pass a signal.
      if ((!getMode().test || signal) && signal.aborted) {
        return Promise.reject(cancellation());
      }

      this.dispatchCustomEventForTesting(AmpEvents_Enum.LOAD_START);
      const isLoadEvent = this.layoutCount_ == 0; // First layout is "load".
      this.signals_.reset(CommonSignals_Enum.UNLOAD);
      if (isLoadEvent) {
        this.signals_.signal(CommonSignals_Enum.LOAD_START);
      }

      // Potentially start the loading indicator.
      this.toggleLoading(true);

      const promise = tryResolve(() => this.impl_.layoutCallback());
      this.preconnect(/* onLayout */ true);
      this.classList.add('i-amphtml-layout');

      return promise.then(
        () => {
          if ((!getMode().test || signal) && signal.aborted) {
            throw cancellation();
          }
          if (isLoadEvent) {
            this.signals_.signal(CommonSignals_Enum.LOAD_END);
          }
          this.setReadyStateInternal(ReadyState_Enum.COMPLETE);
          this.layoutCount_++;
          this.toggleLoading(false);
          // Check if this is the first success layout that needs
          // to call firstLayoutCompleted.
          if (!this.isFirstLayoutCompleted_) {
            this.impl_.firstLayoutCompleted();
            this.isFirstLayoutCompleted_ = true;
            this.dispatchCustomEventForTesting(AmpEvents_Enum.LOAD_END);
          }
        },
        (reason) => {
          if ((!getMode().test || signal) && signal.aborted) {
            throw cancellation();
          }
          // add layoutCount_ by 1 despite load fails or not
          if (isLoadEvent) {
            this.signals_.rejectSignal(
              CommonSignals_Enum.LOAD_END,
              /** @type {!Error} */ (reason)
            );
          }
          this.setReadyStateInternal(ReadyState_Enum.ERROR, reason);
          this.layoutCount_++;
          this.toggleLoading(false);
          throw reason;
        }
      );