How to get child controls correct id to client side

I am working on ASP.NET and not using any ASP.NET’s AJAX framework.
Now I am trying to update the contents of the textboxes and dropdowns in the Grid controls cell on client side using (classic JavaScript way)AJAX. But problem I am facing is that controls (textbox, dropdown) which I would like to update when rendered on the client side get prefixed by the User Controls id and row ids.