Method loadElementClass

src/service/extensions-impl.js:316–325

* Returns the promise that will be resolved with the extension element's * class when the extension has been loaded. If necessary, adds the extension * script to the page. * @param {string} elementName * @param {string} version * @return {!Promise }

(elementName, version = DEFAULT_VERSION)

   * @return {!Promise<typeof ../base-element.BaseElement>}
   */
  loadElementClass(elementName, version = DEFAULT_VERSION) {
    return this.preloadExtension(elementName, version).then((extension) => {
      const element = devAssert(
        extension.elements[elementName],
        'Element not found: %s',
        elementName
      );
      return element.implementationClass;
    });
  }

  /**
   * Add an element to the extension currently being registered. This is a