The Deferred module provides syntax enhancement for dealing with asynchronous requests.
Common use cases for Deferreds are:
Multiple IO requests: making more than one IO request at the same time or in a specific order. This usually means dealing with a lot of events and callbacks.
The Deferred module allows you to simply chain the IO calls and have them execute one after the other, or wait for all of them to complete using `Y.when()`.
Long animations: making a complex animation usually requires doing one type of animation after the other. Again, the Deferred module allows you to chain those calls instead of nesting a lot of callbacks.
A Deferred represents the promise of a certain asynchronous action being completed/resolved or failed/rejected.
``` // Send the content of a form with a POST request and after that, request a message to be shown Y.io.postForm('post.php?', '#myform').get('message.html').then(function (e) { Y.one('#foo').setContent(e.responseText); }); ```