Javascript newbie questions

[ktsirig]

Hello all!
I am starting to use JS a couple of days now and mainly I am interested in using it in form validation and to create pop-ups.
I have 2 questions :

1) If a user doesn't have JS enabled, how will I check for empty fields in the form and show an alert box that prompts for corrections?

2) Also, I have seen sites that have the following : There is a link somewhere which works like this : [a] if you have JS enabled, it "recognizes" it and gives a pop-up window when clicked whereas [b] if you don't have JS enabled, it simply acts like a link and opens a new window (not a poup-up one).

Because I am a bit confused, I am staring to think that maybe JS causes more problems than it solves... Should a programmer use it or ,for instance, do a form validation in another page and don't count on the user having JS enabled?