What is the best method to retrieve an array of elements that have a certain class?

I would use document.getElementsByClassName but IE does not support it.

So I tried Jonathan Snook's solution:

function getElementsByClassName(node, classname) {

    var a = [];

    var re = new RegExp('(^| )'+classname+'( |$)');

    var els = node.getElementsByTagName(*);

    for(var i=0,j=els.length; i<j; i++)

        if(re.test(els[i].className))a.push(els[i]);

    return a;

}

var tabs = document.getElementsByClassName(document.body,'tab');

...but IE still says:

Object doesn't support this property or method

Any ideas, better methods, bug fixes?

I would prefer not to use any solutions involving jQuery or other bulky javascript.

Update:

I got it to work!

As @joe mentioned the function is not a method of document.

So the working code would look like this:

function getElementsByClassName(node, classname) {

    var a = [];

    var re = new RegExp('(^| )'+classname+'( |$)');

    var els = node.getElementsByTagName(*);

    for(var i=0,j=els.length; i<j; i++)

        if(re.test(els[i].className))a.push(els[i]);

    return a;

}

var tabs = getElementsByClassName(document.body,'tab');

...Also if you only need IE8+ support then this will work:

if(!document.getElementsByClassName) {

    document.getElementsByClassName = function(className) {

        return this.querySelectorAll(. + className);

    };

    Element.prototype.getElementsByClassName = document.getElementsByClassName;

}

Use it just like normal:

var tabs = document.getElementsByClassName('tab');