jQuery ajax完成总是在Wordpress上失败

Question

I have the script below that erases a line on a MySQL database with ajax. When the function is fired the line gets deleted from the database but I am always alerted "FAILED".

function deleteRow(data){
if(confirm("Are you sure that you wish to remove this entry?\nThis cannot be undone")){
    $.ajax({
            type: "POST",
            url: "/wp-content/themes/Rexmed/deleterow.php",
            data: {id: data},
            dataType: "json"
        }).done(function() {
            alert("Success");
        }).fail(function() {
            alert("FAILED");
        });
}
}

This is deleterow.php

<?php
require('../../../wp-blog-header.php');
if(!is_user_logged_in()){
auth_redirect();
die();
}

require ('../../../wp-config.php');
$mysqli = new mysqli(DB_HOST, DB_USER, DB_PASSWORD, DB_NAME);
$id = $_POST['id'];

if ($stmt = $mysqli->prepare("DELETE FROM customers WHERE id=?")) {
$stmt->bind_param("s", $id);
$stmt->execute();
$stmt->close();
}

Answer 1

Change the PHP and return JSON

<?php
    require('../../../wp-blog-header.php');
    if(!is_user_logged_in()){
        auth_redirect();
        die();
    }

    require ('../../../wp-config.php');
    $mysqli = new mysqli(DB_HOST, DB_USER, DB_PASSWORD, DB_NAME);
    $id = $_POST['id'];

    if ($stmt = $mysqli->prepare("DELETE FROM customers WHERE id=?")) {
        $stmt->bind_param("s", $id);
        if ($stmt->execute()) {
            $arr = array('success' => 'true');
        }else{
            $arr = array('success' => 'false');
        }
        $stmt->close();
    }

    echo json_encode($arr);

?>

and

.done(function(data) {
     if (data.success == 'true') {
        alert('you did it');
     }
})