Update dropdown list with ajax

[klemme]

I have one select list, which is populated from the DB like this:

<select name="position" id="position" onChange='itemdisplay(this.value)'>
<option value="<?php echo $til_subject; ?>"><?php echo $current_subject; ?></option>
<?php 
while($row=mysqli_fetch_array($result)){
echo '<option value=' . $row['id'] . '>' . $row['linknavn'] . '</option>';	
}
echo "</select>";
?>

// Next to this list i have the other dropdown which depends on whatever is selected in the first one: Which I dont know how to update with ajax..I need to go around the database somehow, after the first list is set.
<select name="page_position" id="page_position">
    <option>- Choose a position -</option> // HELP NEEDED HERE...
    <option value=""></option> // HELP NEEDED HERE...
    </select>

I then want to, after the user have chosen a subject from the select list, populate another dropdown list with the positions available under the specific subject. This info is also taken from the Database.

I havent used AJAX ever before, so is probably wrong here and there.
This is my ajax file, which I include in the page:

// JavaScript Document
function MakeRequestObject(){
var xmlhttp=false;
try {
xmlhttp = new ActiveXObject('Msxml2.XMLHTTP');	
} catch (e) {
try {
xmlhttp = new ActiveXObject('Microsoft.XMLHTTP');
} catch (E) {
xmlhttp = false;
}
}
if(!xmlhttp && typeof XMLHttpRequest!='undefined'){
xmlhttp = new XMLHttpRequest();	
				}
return xmlhttp;
}
		
function itemdisplay(cat){
var xmlhttp=makeRequestObject();
	xmlhttp.open('GET', 'rediger.php?&page_position='+cat, true);
		xmlhttp.onreadystatechange=function(){
			if(xmlhttp.readyState==4 && xmlhttp.status==200){
				var content = xmlhttp.responseText;
					if ( content ) {
							document.getElementById('page_position').innerHTML = content	
				}
		}
	}
	xmlhttp.send(null)
}

I am not sure if i am writing the xmlhttp.open correctly?

And where do I make the database request, in the js file or in the file with the dropdowns?

Confusion is complete, so hope to from someone who finds this easy :-)

[sam230]

see line 21 you r calling page rediger.php.. in this page you will write your sql queries n output you want.

i suggest u to use ajax function of jquery.. less code n easy to understand.

[Stefano Mtangoo]

Check JS libraries. They simplify AJAX calls to single or two functions.
there is JQuery, Scriptaculous, moo tools et al!