JSFiddle - React, Tailwind, and code Playground

HTML

<!-- Adding the sandboxing attribute to illustrade cross-domain -->
<iframe id="one" sandbox="allow-scripts"></iframe>
<iframe id="two" sandbox="allow-scripts"></iframe>

JavaScript

var frame_one = document.getElementById('one');
var frame_two = document.getElementById('two');

// The parent has to mediate because cross-domain sandboxing
// is enabled when on different domains, plus backwards compatible.
window.addEventListener('message', function (m) {
    // Using an object with a 'frame' property that maps to the ID
    // which could be done as you would like.
    var targetFrame = document.getElementById(m.data.frame);
    targetFrame.contentWindow.postMessage(m.data.message, '*');
}, false);


/**
 * This is just to illustrate what a normal document would look
 * like you should just set the normal 'src' attribute and the
 * string would be the normal HTML of the documents.
 */
frame_two.srcdoc = '<!DOCTYPE html>\
<html>\
<head>\
<scr'+'ipt>\
window.addEventListener("message", function (m) {\
alert("Frame Two Says: " + m.data);\
}, false);\
window.addEventListener("load", function () {\
window.parent.postMessage({frame: "one", message: "Received message from frame two!"}, "*");\
}, false);\
</scr'+'ipt>\
</head>\
<body>\
two\
</body>';

frame_one.srcdoc = '<!DOCTYPE html>\
<html>\
<head>\
<scr'+'ipt>\
window.addEventListener("message", function (m) {\
alert("Frame One Says: " + m.data);\
}, false);\
window.addEventListener("load", function () {\
setTimeout(function () {\
window.parent.postMessage({frame: "two", message: "Received message from frame one!"}, "*");\
}, 1500);\
}, false);\
</scr'+'ipt>\
</head>\
<body>\
one\
</body>';