ajax request is successful, but php is not running

I have a very simple jquery function that sends an Ajax call to a php file that should echo out an alert, but for the life of me, cannot get it to run. For now, I'm just trying to trigger the php to run. Here is the javascript:

function getObdDescription(){

    var $code = document.getElementById("vehicle_obd_code").value;
    var $length = $code.length;


    if($length == 5){
        window.confirm($length);

        $.ajax({ url: '/new.php',
            data: {action: 'test'},
            type: 'post',
            success:function(result)//we got the response
            {
            alert('Successfully called');
            },
            error:function(exception){alert('Exception:'+exception);}
        });
        }
    return false;
}

Here is new.php

<?php
    echo '<script language="javascript">';
    echo 'alert("message successfully sent")';
    echo '</script>';
?>

I'm testing in Chrome, and have the network tab up, and can see that the call is successful, as well, I get the 'Successfully called' message that pops up, so the jquery is running, and the Ajax call is successful. I also know that the url: '/new.php is correct, because when I delete new.php from my server, I get a status "404 (Not Found)" from the console and network tab. I've even test without the conditional if($length ==... and still no luck. Of course, I know that's not the problem though, because I get the 'Successfully called' response. Any ideas?

This isnt the way it works if you need to alert the text, you should do it at the front-end in your ajax success function, follow KISS (Keep It Simple Stupid) and in the php just echo the text . that is the right way to do it.

You should do this:

function getObdDescription() {

    var $code = document.getElementById("vehicle_obd_code").value;
    var $length = $code.length;


    if ($length == 5) {
        window.confirm($length);

        $.ajax({
            url: '/new.php',
            data: {
                action: 'test'
            },
            type: 'post',
            success: function (result) //we got the response
            {
                alert(result);
            },
            error: function (exception) {
                alert('Exception:' + exception);
            }
        });
    }
    return false;
}

In your php

<?php
   echo 'message successfully sent';
?>