如何在jquery serialize（）中为ajax请求包含input type =“file”？

Question

I'm creating an application that has a form with all types of inputs... My problem is when I'm using serialize() it doesn't include the input type file. so how do I send the file to the backend (PHP) using serialize()? And also I don't want to use FormData(). If there is any way please help me...

//register.php

$.ajax({
    url: "ajax/user.ajax.php",
    type: "post",
    dataType: "JSON",
    data: {
            formData: $('#registrationForm').serialize()
        },
    success: function(response) {
       console.log(response);               
    },
});



 //user.ajax.php
   <?php
      require_once (__DIR__."/../include/config.php");
      parse_str($_POST['formData'], $_POST);
   ?>

Error:Failed load response data