Does my web application get cached on user’s browser or it will get re-downloaded every time it is used?
It gets cached, similar to Flash and Silverlight applications. If you need to redownload it, clear the browser’s cache, perhaps make sure it’s completely gone from the Temp directory manually.
On a related note, it’s a good idea to add a version number you can bring up somewhere in your application, so you can verify the browser is running the latest version when you load it.