PHP: Downloading file using jquery Ajax and PHP

I am trying to upload a file to a folder using jQuery Ajax and PHP.

This is the form I use to upload a file.

<form id="data" method="post" enctype="multipart/form-data">
                <textarea name="txtmessage" placeholder="Write your post here"></textarea>
                </br>
                        <label>Subject:</label>
                        <input type="text" id="subcode" name="subcode" placeholder="Enter Subject Code e.g.: BIT304">
                        <br/>
                         <input name="img" type="file" /><br/>
                        <button type="submit" class="btn btn-default" id="btnAddAction" name="submit" value="Submit">Share</button>
                </form>
                <script>
                 $("form#data").submit(function(event){
                      var formData = new FormData($(this)[0]);
                      $.ajax({
                        url: 'formprocessing.php',
                        type: 'POST',
                        data: formData,
                        async: false,
                        cache: false,
                        contentType: false,
                        processData: false,
                        success: function (returndata) {
                            $("#comment-list-box").append(returndata);

                        $("form#data")[0].reset();
                        $("#loaderIcon").hide();
                        },
                        error:function (){}
                      });
                    });
                </script>

and this is formprocessing.php to process the form.

<?php
session_start();
require_once("dbcontroller.php");
$db_handle = new DBController();
$id = $_SESSION['id'];

$subcode = $_POST['subcode'];
$txtmessage = $_POST['txtmessage'];

$file = $_FILES['img']['name'];

if($file != "") {
    $subcode = "General";
    $target = "uploads/";
    $fileTarget = $target.$file;
    $tempFileName = $FILES["img"]["tmp_name"];

    $infile = move_uploaded_file($tempFileName,$fileTarget);

    if($infile){
        $result= mysql_query("INSERT INTO fyp_comment(message, subject, userid, timeDate, image) VALUES('$txtmessage', '$subcode', '$id', now(), '$fileTarget')");
        if($result){
            $insert_id = mysql_insert_id();
        }
    }
}
else{
    $result = mysql_query("INSERT INTO fyp_comment(message, subject, userid, timeDate) VALUES('$txtmessage', '$subcode', '$id', now())");
                if($result){
                  $insert_id = mysql_insert_id();
}
}

?>

However, I could not upload the files to the directory after i submit the form and the other part are not stored in the database. On the other hand, if i submit the form without a file the text are all stored into the database. What did I do wrong in this case? been thinking about this for an hour now . Thanks

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<form id="data" enctype="multipart/form-data">

i think your missing enctype="multipart/form-data" in from,
hope this may help you

jQuery AJAX file upload PHP

use above url to find solution