Method whenDefined

src/polyfills/custom-elements.js:147–163

* Returns a promise that waits until the custom element is defined. * If the custom element is already defined, returns a resolved promise. * * @param {string} name * @return {!Promise }

(name)

   * @return {!Promise<undefined>}
   */
  whenDefined(name) {
    const {Promise, SyntaxError} = this.win_;
    assertValidName(SyntaxError, name);

    if (this.registry_.getByName(name)) {
      return Promise.resolve();
    }

    const pending = this.pendingDefines_;
    let deferred = pending[name];
    if (!deferred) {
      deferred = new Deferred();
      pending[name] = deferred;
    }

    return deferred.promise;
  }

  /**
   * Upgrade all custom elements inside root.