The pure JS implementation selects the DOM based on the class of the CSS

// online reference, modified a part of their own
// the following code, pure JS, requires the browser to support the getElementsByClassName method

 
<script type="text/javascript"> 
function getElementsByClassName(classname,node){ 
node = node || window.document; 
if(node.getElementsByClassName){ 
return node.getElementsByClassName(classname); 
}else{ 
var results = new Array(); 
var elems = node.getElementsByTag("*"); 
for (var i=0;i<elems.length;i++){ 
if(elems[i].className.indexOf(classname) != -1){ 
results[elems.length] = elems[i]; 
} 
} 
return results; 
} 
}; 
</script>