How to wait on the __doPostBack method to complete in javascript?

Question

I am using the __doPostBack method to refresh the UpdatePanel in javascript. I just want to wait for the update panel to get updated and then execute the subsequent javascript code. How do I wait on an asynchronous method to complete before I proceed further with execution (like in my case the asynchronous method is __doPostBack)? I want to simulate something like the way it is doing in C# using Thread.Join() method.