如何知道php文件是否处理ajax请求

Question

I've this code snippet for ajax request:

<script type="text/javascript">
        $(document).ready(function() {
            $('#temp').click(function() {
                var username = $('#un').val();
                $.ajax({
                    url: "inter.php",
                    data: 'user=' + username,
                    cache: false,
                    type: 'GET',
                    success: function(data, textStatus, jqXHR) {
                        if (! data.length === 0) {

                            $('#msg').append('available');
                            $('#sub').removeAttr('disabled');
                        } else {

                            $('#msg').append("Username not available");
                            $('#sub').attr('disabled', 'true');
                        }
                    }
                });
            });
        });
    </script>

and the code in inter.php

<?php

$arr = array('one', 'two', 'three');
if (in_array($_GET['user'], $arr)) {
    echo "Username available";
} else {
    //echo "0";
}
?>

But, every time I'm getting the message Username not available.
Can anybody help? I'm newbie to ajax.

EDIT
$_GET['user']
But the same problem remains.

Answer 1

To debug the code I'd added line:

alert(data + " " + data.length);

after

success: function(data, textStatus, jqXHR) {

and found that I'm getting the proper message from my php file.
Then I found that the problem is with my handler

if(!data.length === 0){

where ! operator is working on only data.length whether I need it to work on whole comparison.
I'd changed it to

if(!(data.length === 0)){

and now it works.