ajaxlistener.js

<script>
(function() {
	var xhrOpen = window.XMLHttpRequest.prototype.open;
	var xhrSend = window.XMLHttpRequest.prototype.send;
	window.XMLHttpRequest.prototype.open = function() {
		this.method = arguments[0];
		this.url = arguments[1];
		return xhrOpen.apply(this, [].slice.call(arguments));
	};
	window.XMLHttpRequest.prototype.send = function() {
		var xhr = this;
		var xhrData = arguments[0];
		var intervalId = window.setInterval(function() {
			if(xhr.readyState != 4) {
				return;
			}
			dataLayer.push({
				'event': 'ajaxSuccess',
				'eventCategory': 'AJAX ' + xhr.method,
				'eventAction': xhr.url + (xhr.method == 'POST' && xhrData ? ';' + xhrData : ''),
				'eventLabel': xhr.responseText
			});
			clearInterval(intervalId);
		}, 1);
		return xhrSend.apply(this, [].slice.call(arguments));
	};
})();
</script>