classList.js

// Element.prototype.classList polyfill
// developed by thednp
// license MIT

if( !('classList' in Element.prototype) ) {
	(function(){
		var className = 'className', add = 'add', classList = 'classList', remove = 'remove', contains = 'contains',
		   prototype = 'prototype', element = 'element';

		// classList definition
      function ClassLIST(elem){
			this[element] = elem;
			this[classList] = elem[classList] = [];
			var classesLIST = elem[className].replace(/^\s+|\s+$/g,'').split(/\s+/);
			for (var i = 0; i < classesLIST.length; i++) {
				this[classList].push(classesLIST[i]);
			}
		}

		// methods
		ClassLIST[prototype][add] = function(classNAME){
			if (this[classList].indexOf(classNAME)<0) {
				this[classList].push(classNAME);
				this[element][className] = this[classList].join(' ');
			}
		};
		ClassLIST[prototype][remove] = function(classNAME){
			var classINDEX = this[classList].indexOf(classNAME); 
			if (classINDEX>-1) {
				this[classList].splice(classINDEX,1);
				this[element][className] = this[classList].join(' '); 
			}
		};
		ClassLIST[prototype][contains] = function(classNAME){
			return this[classList].indexOf(classNAME) > -1;
		};

		Object.defineProperty(Element[prototype], classList, { get: function () { return new ClassLIST(this); } });
	}());
}