WP functions undefined in plugin - php

Question

I am having trouble with a plugin I am writing, the plugin shows a form and the form submits to ajaxupload.php.
Basically in my plugin file:
add_action('plugins_loaded','add_to_menu');
function add_to_menu(){
add_action('admin_menu', 'test_plugin_setup_menu');
}
function test_plugin_setup_menu(){
add_menu_page( 'Test Plugin Page', 'add new entry', 'manage_options', 'test-plugin-link', 'test_init' );
// ,'dashicons-database-add'
}
function test_init(){
//echo "<h1>Hello World!</h1>";
// do_action( 'admin_init' );
include(ABSPATH."/wp-content/plugins/my-plugin/form.php");
}
In form.php I can call wp functions!
<?php
// this works!
echo wp_get_current_user()->user_login;
?>
<form>
...
</form>
<script>
$(document).ready(function(){
$("#my_form").on("submit",function(e){
e.preventDefault();
var sendData = $( this ).serialize();
$.ajax({
url: "../wp-content/plugins/my-plugin/ajaxupload.php",
type: "POST",
data: new FormData(this),
...
</script>
in Ajaxupload.php I can't use any WP constants or functions before submission...
if( !empty($_POST['imgurl']) || !empty($_FILES['image']) )
{
$someform_field = $_POST["name"];
echo wp_get_current_user()->user_login; //this line fails
//then call to wpdb to add data to DB
What should be the correct sequence to make wp functions usable in the ajaxupload.php file?

Answer 1

You have to load the wp-load.php file in your ajaxload.php, which loads all wordpress functions, because your ajaxload.php file is called directly:
<?php
require_once __DIR__ . '/../../../wp-load.php';
$someform_field = $_POST["name"];
$user = wp_get_current_user()->user_login; // should now work
//then call to wpdb to add data to DB