how to add a variable to formData and ajax procedure

<input type='file' name='inpfile' id='inpfile' accept='image/*' hidden>

var clicked;
$('#btnplusa').click(function(){
    clicked = 'a';
    $('#inpfile').click();
});

I want to add clicked variable and proccess it on php side, together with inpfile data.

$('#inpfile').change(function(){
    var file_data = $('#inpfile').prop('files')[0];
    var form_data = new FormData();
    form_data.append('inpfile', file_data, 'clicked', clicked);
    $.ajax({
        url: "banners-pro-btnplus.php",
        type: 'post',
        cache: false,
        contentType: false,
        processData: false,
        data: form_data,
        success: function(data) {
            console.log(data);
        }
    });
});

banners-pro-btnplus.php

$file = $_FILES['inpfile'];

$clicked =  $_POST['clicked'];
echo $clicked;
exit();

Console:

Undefined index: clicked in...

How can I get clicked variable on php side?

Solution

 <!DOCTYPE html>
    <html>
    <head>
        <title></title>
        <script src="https://ajax.googleapis.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
        <script type="text/javascript">
            let clicked
            $(document).ready(function(){

                $('#inpfile').change( function ( ){
                    console.log(clicked)
var file_data = $('#inpfile').prop('files')[0];
     var form_data = new FormData();
        form_data.set('inpfile', file_data , file_data.name );
     form_data.append( 'clicked', clicked);
        $.ajax({
            url: "banners-pro-btnplus.php",
            type: 'post',
            cache: false,
            contentType: false,
            processData: false,
            data: form_data,
            success: function(data) {
                console.log(data);
            }
        });
                })
            })
            function bttn_click(){
                clicked = 'a';

                document.getElementById('inpfile').click();
            }
        </script>
    </head>
    <body>
        <form>
            <input type="file" name="" id="inpfile">
            <button onclick="bttn_click()"  >Browse</button>
        </form>
    </body>
    </html>

You can try this way