The dojo.Deferred module has long been a central component of Dojo, providing a powerful interface for asynchronous operations like HTTP requests. Dojo’s Deferreds are a form of promises, providing a separation of concerns between the mechanics of calling a function and the interface for interacting with the eventual asynchronous future result. Passing callbacks directly to functions tightly couple the interface with asynchronous semantics, but using Dojo’s Deferreds (promises) keeps the concerns separate for robust asynchronous code. Furthermore promises can greatly simplify interaction, allowing one to easily get the eventual result of an operation whether it has already finished, or if it is yet to be finished. While the Deferred module has existed in Dojo for some time, version 1.5 introduces some valuable enhancements.

Continue reading