JSFiddle - React, Tailwind, and code Playground

HTML

<iframe src="http://ecma-international.org/ecma-262/6.0/index.html" id="frame" onload="test()"></iframe>
    <pre id="log"></pre>

JavaScript

var test = function() {
log.textContent =
    Object.prototype.toString.call({[Symbol.toStringTag]: "Test"}) + "\n";
    try {
log.textContent +=
    Object.prototype.toString.call(frame.contentDocument);
    } catch (e) {
        log.textContent += "Oops, cross-origin access to @@toStringTag is still broken :(";
    }
}