The installation of this extension is very simple. Just connect to the Typo3 Extension Repository and download «Page JavaScript Selector» (js_select), located in the backend section.

You can there specify the folder where you will store your JS files (you must manually create this folder). By default, it's fileadmin/js/.

Once the extension is installed, you can specify one or more javascript(s) for each of your pages. This is done through the page headers:

You'll find in the selector all the JS files located in the directory you've set during the install process. Just click on a filename to add it.