I am basically trying to create a small registration form. If the username is already taken, I want to add the 'red' class, if not then 'green'.

The PHP here works fine, and returns either a "YES" or "NO" to determine whether it's ok.

The CSS:

input {

border:1px solid #ccc; } .red {

border:1px solid #c00; } .green {

border:1px solid green; background:#afdfaf; }

The Javascript I'm using is:

$("#username").change(function() {

         var value = $("#username").val();

if(value!= '') { $.post("check.php", { value: value }, function(data){

$("#test").html(data);

if(data=='YES') {
 $("#username").removeClass('red').addClass('green');
} if(data=='NO') {
 $("#username").removeClass('green').addClass('red');
}

}); }
});

I've got the document.ready stuff too... It all works fine because the #test div html changes to either "YES" or "NO", apart from the last part where I check what the value of the data is. Here is the php:

$value=$_POST['value'];

if ($value!="") { $sql="select * FROM users WHERE username='".$value."'"; $query = mysql_query($sql) or die ("Could not match data because ".mysql_error()); $num_rows = mysql_num_rows($query);

if ($num_rows > 0) { echo "NO"; } else { echo "YES"; } }