'deferred.el' is a simple library for asynchronous tasks.
[https://github.com/kiwanami/emacs-deferred]

The API is almost the same as JSDeferred written by cho45. See the
JSDeferred and Mochikit.Async web sites for further documentations.
[https://github.com/cho45/jsdeferred]
[http://mochikit.com/doc/html/MochiKit/Async.html]

A good introduction document (JavaScript)
[http://cho45.stfuawsc.com/jsdeferred/doc/intro.en.html]