Simple filtering for Google tags.

gtm.js

var filterClasses = function(ev) {
    'use strict';
    // Get the classNames associated with the clicked elements and split them into an array at whitespace.
    var classes = ev.toElement.className.split(' ');
    // Filter those classes for a class containing with 'gtm-'
    var filteredClasses = classes.filter(function(thisClass) {
        if (thisClass.indexOf('gtm-') !== -1) return thisClass;
        else return false;
    });
    //If it was a match, return the matching classname as a string, otherwise, return false.
    if (filteredClasses.length > 0) return filteredClasses[0];
    else return false;
};

var gaSend = function(className) {
    'use strict';
    //Send with the gtm-className as the label.  
    ga('send', {
        hitType: 'event',
        eventCategory: 'Links',
        eventAction: 'click',
        eventLabel: className
    });
};
//When the doc is ready.
$(document).ready(function() {
    'use strict';
    //Watch the document for clicks on body a's (fix in case elements/links are generated later.)
    $(document).on('click', 'body a', function(ev) {
        //Get the className 
        var className = filterClasses(ev);
        //If it's not false, send it.
        if (className) gaSend(className);
    });
});