How to return an array from an AJAX call?

Use JSON to transfer data types (arrays and objects) between client and server.

In PHP:

• json_encode
• json_decode

In JavaScript:

• JSON.stringify
• JSON.parse

PHP:

echo json_encode($id_numbers);

JavaScript:

id_numbers = JSON.parse(msg);

As Wolfgang mentioned, you can give a fourth parameter to jQuery to automatically decode JSON for you.

id_numbers = new Array();
$.ajax({
    url:"Example.php",
    type:"POST",
    success:function(msg){
        id_numbers = msg;
    },
    dataType:"json"
});

Have a look at json_encode() in PHP. You can get $.ajax to recognize this with the dataType: "json" parameter.