Chargebee Help Center

Hello Mike

You can certainly listen to the messages without the library. 

Please check this sample code snippet that listens to the messages sent from the iframe.

var eventMethod = window.addEventListener ? "addEventListener" : "attachEvent";
var eventer = window[eventMethod];
var messageEvent = eventMethod == "attachEvent" ? "onmessage" : "message";

// Listen to message from child window
eventer(messageEvent,function(e) {
  // e.data will be json string
  var messObj = JSON.parse(e.data);
  if(messObj.onload){
    // onload callback
  }
  // |||ly check for

  // messObj.resize
  // messObj.onSubmit
  // messObj.success
  // messObj.cancel
},false);