polyfill-service/polyfills/DOMTokenList/polyfill.js

A polyfill combinator

(function (global) {
	var nativeImpl = "DOMTokenList" in global && global.DOMTokenList;

	if (
			!nativeImpl ||
			(
				!!document.createElementNS &&
				!!document.createElementNS('http://www.w3.org/2000/svg', 'svg') &&
				!(document.createElementNS("http://www.w3.org/2000/svg", "svg").classList instanceof DOMTokenList)
			)
		) {
		global.DOMTokenList = _DOMTokenList;
	}

	// Add second argument to native DOMTokenList.toggle() if necessary
	(function () {
		var e = document.createElement('span');
		if (!('classList' in e)) return;
		e.classList.toggle('x', false);
		if (!e.classList.contains('x')) return;
		e.classList.constructor.prototype.toggle = function toggle(token /*, force*/) {
			var force = arguments[1];
			if (force === undefined) {
				var add = !this.contains(token);
				this[add ? 'add' : 'remove'](token);
				return add;
			}
			force = !!force;
			this[force ? 'add' : 'remove'](token);
			return force;
		};
	}());

	// Add multiple arguments to native DOMTokenList.add() if necessary
	(function () {
		var e = document.createElement('span');
		if (!('classList' in e)) return;
		e.classList.add('a', 'b');
		if (e.classList.contains('b')) return;
		var native = e.classList.constructor.prototype.add;
		e.classList.constructor.prototype.add = function () {
			var args = arguments;
			var l = arguments.length;
			for (var i = 0; i < l; i++) {
				native.call(this, args[i]);
			}
		};
	}());

	// Add multiple arguments to native DOMTokenList.remove() if necessary
	(function () {
		var e = document.createElement('span');
		if (!('classList' in e)) return;
		e.classList.add('a');
		e.classList.add('b');
		e.classList.remove('a', 'b');
		if (!e.classList.contains('b')) return;
		var native = e.classList.constructor.prototype.remove;
		e.classList.constructor.prototype.remove = function () {
			var args = arguments;
			var l = arguments.length;
			for (var i = 0; i < l; i++) {
				native.call(this, args[i]);
			}
		};
	}());

}(this));