使用JS重定向到包含在子文件夹中的php中的父页面

Question

I have a PHP file that placed in sub-folder and have an "href" of a parent HTML page echoed as an alert message to redirect to that page after hitting OK.

simply it looks like this:

parent_page.PHP

 /PHP

   file.php

I used all the supposed formats such as ./ or ../ and even a single slash but none of them are working and it redirects me to a page that says : object not found.

here is the actual code

echo"<script type='text/javascript'>
 window.location.href='page_parent.php';
 alert('$message');</script>";

thanks.