track outbound links in Google Analytics

outbound.js

var trackOutboundLink = function(event) {
	var url = this.href;
	ga('send', 'event', 'outbound', 'click', url, {
		'transport': 'beacon',
		'hitCallback': function(){document.location = url;}
	});
	event.preventDefault();
}

Array.prototype.slice.call(document.getElementsByTagName('a')).map(function(el) {
	if (el.href[0] != '/') el.addEventListener('click', trackOutboundLink);
});

For wider Browser support, you may not want to rely on Array.from that is only available in newer browsers ;-) (hi IE11 and Android browser!)

Array.prototype.slice.call(document.getElementsByTagName('a')).map(function(el) {

does the same thing, in all it's ugliness ;)

Good point. Thank you.