Function expectPostMessage

testing/iframe.js:434–447

(sourceWin, targetwin, msg)

 * @return {!Promise<!Object>}
 */
export function expectPostMessage(sourceWin, targetwin, msg) {
  return new Promise((resolve) => {
    const listener = (event) => {
      if (
        event.source == sourceWin &&
        JSON.stringify(msg) == JSON.stringify(event.data)
      ) {
        targetwin.removeEventListener('message', listener);
        resolve(event.data);
      }
    };
    targetwin.addEventListener('message', listener);
  });
}

/**
 * Returns a promise for when the condition becomes true.