How to call server side function in client side in asp.net?

If you mean calling code behind (C# or VB) from javascript, that question has been ask/answered several times in the lasyt 30 days. Search the site - you'll find it.

EDIT ======================

Whoever 1-voted this should consider that we are probably SICK AND TIRED of answering the same question OVER AND OVER AGAIN, especially when a simple search of the site would reveal the answer in a matter of SECONDS. I can understand being too lazy to code a certain way, but being too lazy to do a little casual research on your own indicates to me that you should consider a vocation that doesn't involve anything more complicated than open-mouth breathing.