getElementsByClassName

<script type="text/javascript">
//<![CDATA[

if(typeof document.getElementsByClassName !== 'function') {
  document.getElementsByClassName = function(clsName){
    if(!clsName)
      return [];
    var retVal = [];
    var elements = document.getElementsByTagName("*");
    var expr = new RegExp('(^| )' + clsName + '( |$)');
    for(var i=0 ; i<elements.length ; i++)
        if(expr.test(elements[i].className))
            retVal.push(elements[i]);
    return retVal;
  }
}

//]]>
</script>