Error calling javascript function in html button

I'm trying to call a javascript function on a button in html. Both the button and the javascript function are in the same file, however I am having an error saying that the function is not available.

HTML:

<button onclick="countFiles()">Desencriptar</button>

Javascript:

<script>
function countFiles() {
    $directory = "/uploadFiles";
    $filecount = 0;
    $files = glob($directory . "*");
    if ($files){
    $filecount = count($files);
    }

    if($filecount > 0){
        echo '<script type="text/javascript">',
        'window.location.href = "decrypt.php";',
        '</script>';
    }else{
        echo "<script type='text/javascript'>alert('Precisa de inserir pelo menos 1 ficheiro');</script>";
    }
}   
</script>