Simple PostMessage logger

postmessage_logger.js

function handlePostMessage(e) {
  // The actual message is contained in the data property of the event.
  var msg = JSON.parse(e.data);

  // The message ID is now a property of the message object.
  var msgId = msg.MessageId;

  // The message parameters themselves are in the Values
  // parameter on the message object.
  var msgData = msg.Values;

  console.log(msgId + '\n\n' + JSON.stringify(msgData));

  if(msgId == "App_LoadingStatus"){
    // Handle a specific message here if you want.
  }
}
window.addEventListener('message', handlePostMessage, false);