Track external link clicks with Google Universal Analytics

/**
 * Hook external links to feed data to Google Analytics.
 */
(function () {
    /* Check we have access to `querySelectorAll` and the
     * GA object. This means this code won't run on all
     * browsers. 
     */
    if (!Element.prototype.querySelectorAll || 
        typeof ga === "undefined") {
        return;
    }

    /* `click` event handler to push the event to GA */
    var handler = function(e) {
        var self = this;

        /* Track the event using universal analytics.
         * The old GA call would look like:
         *
         *  _gaq.push(
         *      ['_trackEvent', 
         *       "External Link",
         *       this.href.replace(/^http[s]?:\/\//, '')
         *      ]);
         */

        ga('send', 
           'event', 
           'External Link', 
           'click', 
           this.href.replace(/^http[s]?:\/\//, ''));

        /* If the link opens in the same window, we need a
         * delay to allow the request to go back to GA.
         */
        if ("_blank" != this.target) {
            if (Event.prototype.preventDefault) {
                e.preventDefault();
            }
            setTimeout(function() {
                document.location.href = self.href;
            }, 100);
            return false;
        }
    }

    /* Find all external links and add the handler. This
     * code won't work with IE < 9.
     */
    var links = document.querySelectorAll('.external-link');

    for (var i = links.length - 1; i >= 0; i--) {
        if (Element.prototype.addEventListener) {
            links[i].addEventListener('click', handler);
        }
        else if (Element.prototype.attachEvent) {
            links[i].attachEvent('onclick', handler);
        }
    }
})();