Normally, only the creator of a Deferred should call this method; you can prevent other code from changing the Deferred's state by returning a restricted Promise object through deferred.promise().

When the Deferred is rejected, any failCallbacks added by deferred.then() or deferred.fail() are called. Callbacks are executed in the order they were added. Each callback is passed the args from the deferred.reject() call. Any failCallbacks added after the Deferred enters the rejected state are executed immediately when they are added, using the arguments that were passed to the deferred.reject() call. For more information, see the documentation for jQuery.Deferred().