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* Minimal classList shim
* By Devon Govett
if (!("classList" in document.documentElement)) {
Object.defineProperty(HTMLElement.prototype, 'classList', {
get: function() {
var self = this;
function update(fn) {
return function(value) {
var classes = self.className.split(/\s+/g),
index = classes.indexOf(value);
fn(classes, index, value);
self.className = classes.join(" ");
return {
add: update(function(classes, index, value) {
if (!~index) classes.push(value);
remove: update(function(classes, index) {
if (~index) classes.splice(index, 1);
toggle: update(function(classes, index, value) {
if (~index)
classes.splice(index, 1);
contains: function(value) {
return !!~self.className.split(/\s+/g).indexOf(value);
item: function(i) {
return self.className.split(/\s+/g)[i] || null;

I wonder if those browsers that are missing classList support would have DOMTokenList support, which would be the base proto of classList...

@devongovett Look to how some of the selector engines like Sizzle or NWMatcher detect class names. They have refined them for speed, at first glance yur class name operations look a little costly. Also extending the DOM leads to nothing but headache and dev tears.


That's exactly what it is supposed to be though - a polyfill. And I agree it can probably be improved but it was designed to be really small and I wrote it in about 5 minutes. :) If you've got improvements, by all means have at it.

@devongovett Polyfill or not, extending the DOM has been known to cause problems. Would be better if you made a small utility method that leveraged native functionality or forked for a fallback.


If you don't want to extend the DOM, don't use this shim. What problems do you see? It seems to work for me...

@devongovett I'm trying to save you some heart burn by giving you a heads up. I've spent many years working with libs like Prototype that extend the DOM and a lot of the time things seemed to work fine, for a time, but then fell apart down the road.

I understand support was aimed at IE8/9 but this causes script errors in IE 6/7 and 8.
IE 8 has window.Element but not window.HTMLElement.


It doesn't have Object.defineProperty either... better?


@rwldrn wouldn't length be better implemented as a getter? Otherwise if the user updates the className the length won't change.

@devongovett IE8 has Object.defineProperty. In fact, IE8's Object.defineProperty only works on DOM elements ;D


Yeah I realize that. I was referring to IE 6 and 7. Unfortunately the length getter wouldn't work in IE 8 either.

@devongovett In IE8 HTMLElement will be an undefined var reference and throw an error.

Also another heads up, String#split and IE are iffy when it comes to regexp support (rule of thumb: keep it really simple and test).
Your regexp could be simplified to just /\s+/.

@devongovett - it sure would, but like I said it's "half-assed" and only meant to work in IE8 right?


Eh! Screw IE < 9. Too many problems and I wasn't trying to support it in my app anyway. The regex is now simplified, and I added "real" length support via a getter. And to answer your question @rwldrn, it looks like IE does not have DOMTokenList.


Super late to this party, but my classList polyfill has true native .length by being an array (i.e. constructor's .prototype = []). You could try something like that.

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