Fire a one-way ajax call
Only time it will matter is if the request to the server is not complete. You should check to make sure the call is at a readyState value of 2 [aka sent], before exiting.
I would just perform a call with no callback, I don't believe there is a property that allows the F&F method.
for a very short ajax call you could try the following code as an alternative, if you wanted.
$.get('URL');