JSFiddle - React, Tailwind, and code Playground

HTML

<iframe id="iframe" src="about:blank">
</iframe>

JavaScript

function z() {
  alert(window.name);
}

window.name = 'w top';
z();

var iframe = document.getElementById('iframe');
iframe.contentWindow.name = 'w iframe';

iframe.contentWindow.z = z;
iframe.contentWindow.z();