ajax调用未发送到php

My ajax call won't send to php file for it to show on screen. The call is running because i get the "ok" alert but the php page does not show the hello world on the screen

    $.ajax({

        type: "POST",
        url: "test.php",
        data: {data: "hello world"},
        success: function(){
            alert("OK");
        }
    });


    $test = 7;
    echo $test;
    $data = "";
    $data = $_POST["data"]; 
    $request = $data;

    print_r($request);
    echo $request;

expected: 7hello world actual: 7

You need a callback in your function .. IE

success: function(result){

This will end up with the output of the php file, and can be used like so:

alert("OK - " + result);
// OR
console.log(result);
// OR
$('#your_element_id').html(result);