pardot-custom-thank-you.js

	var origin = document.referrer.replace(/^((\w+:)?\/\/[^\/]+\/?).*$/,'$1').replace(/\/$/, '');
	try {
		parent.postMessage('pardot_form_success', origin);
	} catch (e) {
		window.console && window.console.log(e);
	}

With whitelisting

	var parentOrigin = document.referrer.replace(/^((\w+:)?\/\/[^\/]+\/?).*$/,'$1').replace(/\/$/, '');
	var allowedOrigins = [
		'https://nowak.click',
		'https://testucan.net'
	];
	try {
		if (!allowedOrigins.includes(parentOrigin)) {
			throw new Error(parentOrigin + ' is not whitelisted.');
		}
		parent.postMessage('pardot_form_success', parentOrigin);
	} catch (e) {
		window.console && window.console.log(e);
	}