JSFiddle - React, Tailwind, and code Playground

HTML

<iframe src="http://fiddle.jshell.net/zTctZ/show/" id="frame1"></iframe>

JavaScript

var frame1_window = document.getElementById("frame1").contentWindow;
frame1_window.onmessage = function(e) {
    alert(e.data);
};
frame1_window.postMessage("Hello from same domain", "http://fiddle.jshell.net");