window.addEventListener('message', function (evt) {
  var msg = evt.data;
  // var origin = evt.origin;  // TODO: Check origin.
  var type = msg.type;
  var data = msg.data;
  console.log('[client] Message received:', msg);
  if (type === 'response') {
    var action = data.action;
    if ('height' in data) {
      var height = data.height;
      this.iframe.style.height = height + (/^\d+$/.test(height) ? 'px' : '');
    }
  }
});