1. Giving the user more control over the browser.
2. Detecting the user's browser and OS. The ability to detect the user's browser and OS allows your script to perform platform-dependent operations, if necessary.
3. Performing simple computations on the client side.
4. Validating the user's input.
5. Handling dates and time.
Example 2. This script says "Nice morning, isn't it?" or "Good afternoon!" or "Good evening!" or "Wow, you are not asleep yet!?" depending on the current time. It also tells you today's date.
6. Generating HTML on the fly.