JSFiddle - React, Tailwind, and code Playground

HTML

<!-- If the remote system is NOT under your control, it CANNOT respond with the X-Frame-Options header set to SAMEORIGIN or DENY! -->
<iframe id="inlineframe" src="http://www.randomwebsite.com" frameborder="0" scrolling="auto" width="800" height="300" marginwidth="5" marginheight="5" ></iframe>

JavaScript

//Depending on the JS you put here, you may get some "unsafe Javascript" warnings from certain browsers
~function()
{
    var frame = document.getElementById('inlineframe'),
        ref = frame.contentWindow ? frame.contentWindow.document : frame.contentDocument;
    
    // ref is now a reference to the document of the content within the iframe
    // You can now do your getElementById/getElementByTagName etc. and otherwise
    // manipulate the response as you please.
    console.log(ref);
}();