how can i populate mutiple value in combobox through ajax?

Your question is quite vague, and to my understanding, I don't know how much you know about AJAX which makes it even more difficult.

If you knew the basics for AJAX, a request is made, a response is received, in that response is possibly the data to populate a multiple value combo-box and from there you would just create the DOM for it and add it into the site.

You might not even need AJAX for it, if you stored the values you wanted to change within javascript, then you could easily just call upon them, but if you do require AJAX to do the request, possibly because it's got to grab it from a database, then that might be why you'd need it.

I only outlined the basics, but I do think you're wanting more.

Cheers,

MC

What I think you are looking for is something like

<form name="testform">
<select name="testselect">
	<option value="first">first option</option>
	<option value="second">second option</option>
	<option value="third">third option</option>
	<option>your browser can't handle this script</option>
</select>
</form>

<script>
document.forms['testform'].testselect.options[i] = new Option('new text','new value');
</script>

There is a whole turotial on this at http://www.quirksmode.org/js/options.html