Project Hosting is actually a sub-directory of Google Code, the main purpose of which is for developers to upload open-source softwares for sharing. If you upload your .js files over there, you have to agree that it will be available for download to everyone.
1. Login at Google Code using your Google account.
2. Go to 'Project Hosting on Google Code' webpage, or simply click here.
3. Click 'Create a new project'.
4. A new webpage will appear. Fill up all the necessary information and then click the 'Create project' button.
5. Click the 'Downloads' tab and then 'new download'.
6. Fill up the needed information. Browse for your .js file, attach and then click 'Submit file'.
7. If you want to link to the file immediately, just right-click on the file name and select 'Copy Link Location'.
8. Paste the URL to the script for your blog or website (see the sample below), save and your done.
The great advantage for .js files being hosted on Google Code is that it loads faster, more specially if you're on Blogger, and of course it is free.