I found the following regex from another Stack Overflow question: Change an element's class with JavaScript

And have used it in part of my script with success, however in another it seems to be failing.

I threw together a very minimalist test case on jsFiddle, and it is also failing:

http://jsfiddle.net/ew47Y/1/

HTML:

<div class=foo id=foo>

    hello

</div>​

JS:

$(document).ready(function(){

     foo = document.getElementById('foo');

     foo.className += ' bar foobar';

     alert(foo.className);

     foo.className.replace( /(?:^|s)bar(?!S)/ , '' )

     alert(foo.className);

})​