I'm using XAMPP and opening my html file using localhost/filename.html. So both my html document and .js file are in the same directory, in C:/xampp/htdocs. When I open the html file using localhost/filename.html in the browser window, it does not include the changes to the code. It's using the same version of the .js file before I saved the changes. But when I open the html document locally (offline, not running on localhost), the changes to the .js are there.
But at first you have to set/change the MySQL Root password. Start the Apache server and type localhost or 127.0.0.1 in your browser's address bar. If you haven't deleted anything from the htdocs folder the xampp status page appears. Navigate to security settings and change your mysql root password.
(You may run phpinfo.php to know your settings (you can create a simple script file with that name , check for extension_path. It should point to the 'php\ext' folder (that's where mine is)) I set the path in php.ini to c:\xampp\php\ext. You can get to this file from the XAMPP control panel by clicking on CONFIGURE button corresponding to APACHE web server then, select 'php.ini' from the pop list. Search for extension_path and remove the comment directive (';').
XAMPP isn't in PortableApps.com Format, but it easily integrates with the PortableApps.com Menu by using the XAMPP Launcher (linked above) and installing XAMPP in the root directory of your portable device or creating an XAMPP\App\xampp directory within the launcher path and placing it there. The root directory is preferred. You can open the zip/7z archive of the portable version with 7-Zip Portable.