turn caching off for certain file extensions in IIS7

1. open IIS7 and click on a site
2. from the big icons that appear in the main window, pick the "Output Caching" icon and double-click upon it
3. you will end up in an "Output Caching" screen where you should click the "Add..." link
4. type a file extension (such as ".js") in the first fill-in-the-blank box and then complete the rest of the dialog box