Method toggleFallback

src/custom-element.js:1972–1999

* Hides or shows the fallback, if available. This function must only * be called inside a mutate context. * @param {boolean} show * @package @final

(show)

     * @package @final
     */
    toggleFallback(show) {
      assertNotTemplate(this);
      const resourceState = this.getResource_().getState();
      // Do not show fallback before layout
      if (
        !this.R1() &&
        show &&
        (resourceState == ResourceState_Enum.NOT_BUILT ||
          resourceState == ResourceState_Enum.NOT_LAID_OUT ||
          resourceState == ResourceState_Enum.READY_FOR_LAYOUT)
      ) {
        return;
      }
      // This implementation is notably less efficient then placeholder
      // toggling. The reasons for this are: (a) "not supported" is the state of
      // the whole element, (b) some relayout is expected and (c) fallback
      // condition would be rare.
      this.classList.toggle('amp-notsupported', show);
      if (show == true) {
        const fallbackElement = this.getFallback();
        if (fallbackElement) {
          Services.ownersForDoc(this.getAmpDoc()).scheduleLayout(
            this,
            fallbackElement
          );
        }
      }
    }

    /**
     * An implementation can call this method to signal to the element that