<form method="post" action="" enctype="multipart/form-data">
    <label>File Input: <input type="file" name="file" id="demo1" /></label>
</form>

var interval;
    var $upload="uploaded.php";
            
            function applyAjaxFileUpload(element) {
                $(element).AjaxFileUpload({
                    action: $upload,
                    onChange: function(filename) {
                        // Create a span element to notify the user of an upload in progress
                        var $span = $("<span />")
                            .attr("class", $(this).attr("id"))
                            .text("Uploading")
                            .insertAfter($(this));
...
}

            applyAjaxFileUpload("#demo1");

$whitelist = array('jpg', 'jpeg', 'png', 'gif');
$name      = null;
$error     = 'No file uploaded.';


if (isset($_FILES)) {
    if (isset($_FILES['file'])) {
        $tmp_name = $_FILES['file']['tmp_name'];
        $name     = basename($_FILES['file']['name']);
        $name      = $cart_qties.'___'.$name;
        $error    = $_FILES['file']['error'];
        
        if ($error === UPLOAD_ERR_OK) {
            $extension = pathinfo($name, PATHINFO_EXTENSION);

            if (!in_array($extension, $whitelist)) {
                $error = 'Invalid file type uploaded.';
            } else {
            move_uploaded_file($tmp_name, 'upload/'.$name);
            }
        }
    }
}

echo json_encode(array(
    'name'  => $name,
    'error' => $error,
));
die();