Tracking WordPress Data in Google Analytics

functions.php

<?php

/**
 * Enqueue ga.js and pass PHP variables into it
 */

function ga_script_enqueuer() {

    wp_enqueue_script('ga', get_template_directory_uri() . 'ga.js');

    if (is_user_logged_in()) {
        $user = wp_get_current_user();
        $ga_user_data = array(
            'username' => $user->user_login
        );
    }

    if (isset($ga_user_data)) {
        wp_localize_script('ga', 'User', $ga_user_data);
    }

}
add_action('wp_enqueue_scripts', 'ga_script_enqueuer');


/**
 * Redirect user to custom URL after comment submission
 */
 
function redirect_after_comment($location) {
    $location = $location . '?submitted=1';
    return $location;
}
add_filter('comment_post_redirect', 'redirect_after_comment');

?>

ga.js

/**
 * Get URL parameters
 * http://www.onlineaspect.com/2009/06/10/reading-get-variables-with-javascript/
 * 
 * @param  {string} q Name of the parameter to get
 * @param  {string} s Static URL as string to get the parameters.
 *                    Leave empty to get current window location.
 * @return {string}   Value of variable
 */
 
function $_GET(q, s) {
    s = s ? s : window.location.search;
    var re = new RegExp('&'+q+'(?:=([^&]*))?(?=&|$)','i');
    return (s=s.replace(/^\?/,'&').match(re)) ? (typeof s[1] == 'undefined' ? '' : decodeURIComponent(s[1])) : undefined;
}


/**
 * Google Analytics Base Code
 */

(function(i,s,o,g,r,a,m){i['GoogleAnalyticsObject']=r;i[r]=i[r]||function(){
(i[r].q=i[r].q||[]).push(arguments)},i[r].l=1*new Date();a=s.createElement(o),
m=s.getElementsByTagName(o)[0];a.async=1;a.src=g;m.parentNode.insertBefore(a,m)
})(window,document,'script','//www.google-analytics.com/analytics.js','ga');

ga('create', 'UA-XXXXXXXX-Y', 'auto');


/**
 * Custom Dimension
 */
 
if (typeof User === 'object') {

    var username = User.username;

    if (username) {
        ga('set', 'dimension1', username);
    }

}

ga('send', 'pageview');


/**
 * Custom Event
 */
 
document.addEventListener('DOMContentLoaded', function(event) {

    // #important_btn click
    var importantBtn = document.getElementById('important_btn');

    importantBtn.addEventListener('click', function() {
        ga('send', 'event', 'button', 'click', 'Important Button');
    });

});