The new specification has been out there for a little while and Google Chrome (13+) has already adopted this.

Try document.createElement('div').cssList and look at the __proto__:

• add
• contains
• remove
• toggle
• .. more

I see two possible implementations:

• in the method (ie. addClass) feature detection decides one or the other
• a private or local group of methods is introduced that are set by reference to the native api if possible, and fallback to utility functions.

The latter is a bit more work, but better for performance.

ie.

class = {

add: elem.cssList ? elem.cssList.add : function( className, el ) { ... },

remove: elem.cssList ? elem.cssList.remove : function( className, el ) { ... }

}

and use like class.add.appy( elem, str );

A bit like isArray so to say (set by reference)