How can I include all JavaScript files in a directory via JavaScript file?

In general, this is probably not a great idea, since your html file should only be loading JS files that they actually make use of. Regardless, this would be trivial to do with any server-side scripting language. Just insert the script tags before serving the pages to the client.

If you want to do it without using server-side scripting, you could drop your JS files into a directory that allows listing the directory contents, and then use XMLHttpRequest to read the contents of the directory, and parse out the file names and load them.

Option #3 is to have a "loader" JS file that uses getScript() to load all of the other files. Put that in a script tag in all of your html files, and then you just need to update the loader file whenever you upload a new script.

What about using a server-side script to generate the script tag lines? Crudely, something like this (PHP) -

$handle = opendir("scripts/");

while (($file = readdir($handle))!== false) {
    echo '<script type="text/javascript" src="' . $file . '"></script>';
}

closedir($handle);