add/remove/hasclass in plain js

helper.js

var hasClass, addClass, removeClass;
if ('classList' in document.documentElement) {
    hasClass = function (el, className) { return el.classList.contains(className); };
    addClass = function (el, className) { el.classList.add(className); };
    removeClass = function (el, className) { el.classList.remove(className); };
} else {
    hasClass = function (el, className) {
        return new RegExp('\\b'+ className+'\\b').test(el.className);
    };
    addClass = function (el, className) {
        if (!hasClass(el, className)) { el.className += ' ' + className; }
    };
    removeClass = function (el, className) {
        el.className = el.className.replace(new RegExp('\\b'+ className+'\\b', 'g'), '');
    };
}