3 ways to ajax sequentially

One is to chain ajax calls through callbacks (have your Ajax callback go to a handler that starts the next ajax request). This is the simplest implementation but deep call chain will cause maintenance headache due to tightly coupling. It is serial requests and serial responses.

The second method is to have a class to manage a queue of requests, and process them sequentially. The sexy.js does parallel requests and serial responses. The library might be of this solution.

The third way is jQuery Deferred to force async functions to execute sequentially by using its pipe chaining http://api.jquery.com/category/deferred-object/. jQuery 1.5 starts to implement Promise/A spec and provides a bunch of interfaces like when(), done(), fail(), then(), reject(), and resolve() etc.