PHP“上传文件”代码不起作用

Question

HTML in 'index.php':

<form action="index.php" method="post" enctype="multipart/form-data">

    <input type="file" name="fileToUpload" id="fileToUpload" accept="application/pdf, .pdf" required><br>

    <input type="submit" name="submit" value="SUBMIT">

</form>

PHP in 'index.php':

<?php

    if (isset($_POST['submit'])) {

        $target_dir = 'docs/';
        $temp_loc = $_FILES['fileToUpload']['tmp_name'];
        $file = $_FILES['fileToUpload']["name"];

        if(move_uploaded_file($temp_loc,$target_dir.$file)) {
            ?><script>alert('successfully uploaded');</script><?php
        } else {
            ?><script>alert('error while uploading file');</script><?php
        } 
    }

?>

The following code doesn't seem to upload any of the documents I select to the target dircetory, that is, '/docs'.

I'm using wampserver with localhost, if that is needed at all. The 'file-upload' is allowed in the 'php.ini'

I've seen many tutorials and have even done troubleshooting on Stackoverflow itself, but I can't seem to make it work.

Thanks in advance