So file uploading was actually working fine initially, but in order to protect my PHP files I did URL rewrite in htaccess and the file uploading has stopped ever since... I removed the htaccess redirect rule and it began working again. Please come to my aid because I really need to hide the actual directory to my PHP files.
javascript ajax request
var form = new FormData();
form.append("file_name", file);
AJAX_REQUEST.open("POST", " https://my_site.com/testFile", true);
AJAX_REQUEST.send(form);
htaccess file
RewriteEngine On
RewriteCond %{HTTPS} off
RewriteRule ^(.*)$ https://%{HTTP_HOST}%{REQUEST_URI} [L,R=301]
RewriteRule ^testFile https:///my_site.com/phps/validateFile.php [NC,L]