Method constructor

third_party/subscriptions-project/swg.js:10239–10254

* @param {!Document} doc * @param {!Object =} attrs

(doc, attrs = {})

   * @param {!Object<string, string|number>=} attrs
   */
  constructor(doc, attrs = {}) {
    const mergedAttrs = Object.assign({}, friendlyIframeAttributes, attrs);

    /** @private @const {!HTMLIFrameElement} */
    this.iframe_ = /** @type {!HTMLIFrameElement} */ (
      createElement(doc, 'iframe', mergedAttrs)
    );

    // Ensure that the new iframe does not inherit any CSS styles.
    resetAllStyles(this.iframe_);

    /** @private @const {!Promise} */
    this.ready_ = new Promise((resolve) => {
      this.iframe_.onload = resolve;
    });
  }

  /**
   * When promise is resolved.