Dealing with classes (add, remove, has). Source: http://blog.ponyfoo.com/2013/07/09/getting-over-jquery

classes.js

!function(exports){
    var class_list = !!document.body.classList;
    var s = '(\\s|^)'; // space or start
    var e = '(\\s|$)'; // space or end

    function getRegex(className){
        return new RegExp(s + className + e, 'g');
    }

    exports.addClass = function(element, className){
        if(class_list){
            element.classList.add(className);
        }else{
            element.className += ' ' + className;
        }
    };

    exports.removeClass = function(element, className){
        if(class_list){
            element.classList.remove(className);
        }else{
            var rclass = getRegex(className);
            element.className = element.className.replace(rclass, '');
        }
    };

    exports.hasClass = function(element, className){
        if(class_list){
            return element.classList.contains(className);
        }else{
            var rclass = getRegex(className);
            return element.className.match(rclass);
        }
    };
}(window);