Ajax jquery file problem

[CSS-Regex]

I am not able to get this to work at all.

<div id="container">
        <form id="myform" method="POST" enctype="multipart/form-data">
            <div class="textInput">
                <input type="file" name="file" id="file">
            </div>
            <button type="submit" id='btn' value="Submit">Add Photo</button>        
        </form>
    </div>
    <script>
        $(document).ready(function(){
            $('#btn').click(function (e) {
            e.preventDefault();
            let formData = new FormData();
            let file = $('#file')[0].files[0];
            formData.append('file', file);
            $.ajax({
                url: 'upload.php',
                type: 'post',
                contentType: false,
                processData:false,
                success: function(data){
                    if (data != 0){
                        alert('success' + data);
                    } else {
                        alert('error');
                    }
                 },
                });          
           });
        })
    </script>

I have tried other methods, but this is not succeeding

the upload.php file is as follows

<?php
$filename = $_FILES['file']['name'];
$location = '/upload/'.$filename;
if (move_uploaded_file($_FILES['file']['tmp_name'], $location)){
    echo $location;
} else {
    echo 0;
}

 

[CSS-Regex]

I've solved the problem of what it says in the <b> tag elements, I had to put 

isset()

Around the $_FILES global variables

I'm still getting an error though, where it should upload the file

[CSS-Regex]

I have an issue with the php code