Add Blesta Affiliate ID to all links on page

blesta-affiliate-id.php

add_action( 'wp_head', function () { ?>
<script>
	function getParameterByName(name, url) {
		if (!url) url = window.location.href;
		name = name.replace(/[\[\]]/g, '\\$&');
		var regex = new RegExp('[?&]' + name + '(=([^&#]*)|&|#|$)'),
			results = regex.exec(url);
		if (!results) return null;
		if (!results[2]) return '';
		return decodeURIComponent(results[2].replace(/\+/g, ' '));
	}
	window.onload = function() {
		var anchors = document.getElementsByTagName("a");
		let affiliate_id = getParameterByName('a');
		if (affiliate_id !== null ) {
			let blestadomain = '.presswizards.com';
			let daystoexpire = 60;
			const d = new Date();
			d.setTime(d.getTime() + (daystoexpire*24*60*60*1000));
			document.cookie = "affiliate_code=" + affiliate_id + "; expires=" + d.toUTCString() + "; ;domain=" + blestadomain + ";path=/";
			console.log('Set cookie - affiliate ID: ' + affiliate_id + '; expires: ' + d.toUTCString() + '; domain: ' + blestadomain);
			for (var i = 0; i < anchors.length; i++) {
                anchors[i].href = anchors[i].href.indexOf('#') != -1 ? anchors[i].href : anchors[i].href += anchors[i].href.indexOf('?') != -1 ? "&a=" + affiliate_id  : "?a=" + affiliate_id;
            }
			fetch('https://billing.presswizards.com/order/forms/a/' + affiliate_id, { mode: "no-cors" });
		}
	}
</script>
<?php }, 21 );