This project/page is simply a test harness to listen to messages sent from a parent page when this page is enbedded in an iframe. It was originally created to test message passing in a VS code extension.
If you have this project embedded in an iframe like this:
<iframe id="armvizFrame" src="https://windowmessages.azurewebsites.net/index.html"></iframe>
You can use this code to send messages to the child frame:
const webFrame = document.getElementById('myframe');
webFrame.contentWindow.postMessage({ foo: 'bar' }, '*');