JSFiddle - React, Tailwind, and code Playground

JavaScript

var iframe = document.createElement('iframe'),
		html = '<html> <head></head> <body> //contents </body> </html>',
		newurl = "https://www.facebook.com/",
		basehref = "<base href='" + newurl + "'>",
		n = html.indexOf("</head>");

var newhtml = [html.slice(0, n), basehref, html.slice(n)].join('');

document.body.appendChild(iframe);
iframe.contentWindow.document.open();
iframe.contentWindow.document.write(newhtml);
iframe.contentWindow.document.close();

console.log(newhtml);