classList polyfill // returns a token list of the class names attached to the element.

Element.classList.js

// classList | @jon_neal | MIT/GPL2
this.Element && !document.lastChild.classList && (function () {
	Object.defineProperty(Element.prototype, "classList", {
		configurable: true,
		get: function () {
			var
			join = [].join,
			push = [].push,
			splice = [].splice,
			node = this,
			list = new function DOMTokenList() {
				var list = this, index;

				list.contains = function (value) {
					var length = list.length;

					index = -1;

					splice.apply(list, [0, length].concat((node.getAttribute("class") || "").split(/\s+/)));

					while (++index < length) if (list[index] == value) break;

					return index < length;
				};

				list.add = function (value) {
					if (!list.contains(value)) push.call(list, String(value));

					node.setAttribute("class", join.call(list, " "));
				};

				list.remove = function (value) {
					if (list.contains(value)) splice.call(list, index, 1);

					node.setAttribute("class", join.call(list, " "));
				};

				list.toggle = function (value) {
					list.contains(value) ? splice.apply(list, [index, 1]) : push.call(list, String(value));

					node.setAttribute("class", join.call(list, " "));
				};

				list.contains("");
			};

			return Object.defineProperties(node, {
				className: {
					configurable: true,
					get: function () {
						return join.call(list, " ");
					},
					set: function (value) {
						this.setAttribute("class", value);

						list.contains("");
					}
				},
				classList: {
					configurable: true,
					get: function () {
						return list;
					}
				}
			}).classList;
		}
	});
})();