Forms Data Controls :: Capture Value Of Javascript Function Called By GridView Linkbutton Click?

i have gridview with linkbutton.when i click linkbutton it should call javascript function which returns value would be input for database functions. how do i capture javascript function retun value(i am using Registerclientscriptblock)? and that should be input for database function. Inshort i need to call two function from link button click - one javascript function,one ado.net function which will update value in database. output of javascript function will be input for database function.

function Getlogitudelantitude(address)
{
return "35.3434343,-74.334343"
}
Linkbutton_click(object sender,Eventargs e)
{
register javascript function .. which should return value
string s = "35.34343,-74.334343"
then call database function(s) - does database operation
}
}