asp.net server controls

how to block the control transfer to server when the validation using java script not satisfied.?
I have a function in client side called validate().The invocation
of this function is taking place in the client side.i.e onclick ="validate();".My problem is this validate function should block
the control transfer to the server when the condition does not met.
Now i am doing my project in asp.net (web based).Server client
also perform some operation.What i want is client side function
should block the control transfering to the server.Please Help me
Thanks in advance
just don't submit the page.
return false on the onSubmit function after checking for validate
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ASP.Net 2.0 Membership II : LoginView Control - Shalvin