Christian Heilmann

How to get all IDs and classes used in a document?

Monday, August 4th, 2008 at 11:46 pm

This was a question from one of the attendees of my JavaScript course, and here is one solution:

 function getIDsAndClasses(elm,parent){
   var elm = elm || '*';
   if(typeof parent !== 'undefined'){
     if(typeof parent === 'string'){
       var parent = document.getElementById(parent) || document;
   } else {
     var parent = document;
   var elms = parent.getElementsByTagName(elm);
   var ids = [];
   var classesFilter = {};
   var i = elms.length;while(i--){
     if(elms[i].id !== ''){
     if(elms[i].className !== ''){
       var singles = elms[i].className.split(' ');
       var j = singles.length;while(j--){
         classesFilter[singles[j]] = singles[j];
   var classes = [];
   for(var i in classesFilter){
   return {ids:ids,classes:classes}

You can call this method either with no parameters or filter it down by providing an element name and a parent element. The parent element could be a DOM reference or a string, both work.

In any case, the output is an object with a property of ids containing an array of ID names and a property called classes with an array of class names.

The script filters out duplicate classes and gets all applied classes – provided they are space separated.

You can see it in action (in the FireBug console) here: Test getIDsAndClasses

I tried using regex to get the IDs and classes, but that turned out to be a mess in JavaScript.

Any faster way?

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