Test-Driving JavaScript Applications

Server-Side Callbacks

A caller of a synchronous function blocks until it gets the result or the intended action is completed. But calls to asynchronous functions are nonblocking. A caller of such functions typically sends one or more callback functions as extra parameters and moves on. Asynchronous functions that use callbacks eventually invoke one or more callbacks when the processing is completed. It’s through these callbacks that they indirectly send a response back to the caller. The difference in the nature of the functions poses some challenges from the point of view of testing.

Due to the nature of the call, a test for a synchronous function automatically waits for the result to arrive. The test for an asynchronous function needs to ...