Help: code isn't working

[lalabored]

I'm really new to Ajax (I just started today). My code below isn't working... can somebody tell me why? Basically what it's supposed to do is it deletes a wall post from the database then it updates the div "wall_posts".

 

<script>

function ajaxFunction()
{
var xmlHttp=null;
try
{
// Firefox, Opera 8.0+, Safari
xmlHttp=new XMLHttpRequest();
}
catch (e)
{
// Internet Explorer
try
{
xmlHttp=new ActiveXObject("Msxml2.XMLHTTP");
}
catch (e)
{
xmlHttp=new ActiveXObject("Microsoft.XMLHTTP");
}
}
return xmlHttp;
}

function delete_wall_post(id,user){
var ajax = ajaxFunction();
if(ajax=null){
alert("Your browser does not support Ajax!");
return;
}
ajax.onreadystatechange=function(){
if(ajax.readyState==4){
var display = document.getElementById('wall_posts');
display.innerHTML = ajax.responseText;
}
}
var url = "wall_delete.php";
url = url + "?id=" + id + "&user=" + user;
ajax.open("GET", url, true);
ajax.send(null);
}
</script>

 

This is my delete link...

 

<a href="javascript: if(confirm('Are you sure?')){ delete_wall_post(<?php echo $row['id']; ?>,'<?php echo $_GET['user']; ?>')}">Delete</a>