Make the Best Use of Asynchronous Callbacks
http://www.ibm.com/developerworks/web/library/wa-aj-async.html?S_TACT=105AGX08&S_CMP=EDU

Mertz, David
IBM
2007

Abstract:

It takes some finesse to make the best use of asynchronous callbacks for Ajax data sources in JavaScript applications. This tip discusses why you should use asynchronous callbacks for Ajax data sources and gives examples of coordinating the readiness of mutually dependent application data sources that may become ready at undefined times with asynchronous calls.