jQuery.Deferred provides a promise property as a function. The default of the most popular alternative libraries is to provide a promise property as an object. _.result provides an easy solution to both cases.

References:

* [jQuery.Deferred](http://api.jquery.com/deferred.promise/)
* [Q.defer](https://github.com/kriskowal/q/wiki/API-Reference#qdefer)
* [when.defer](https://github.com/cujojs/when/wiki/Examples#whendefer)