Deferred objects

Deferred objects and their promises allow us to react to the completion of long-running tasks with a convenient syntax. They are discussed in detail in Chapter 11, Advanced Effects.

Object creation

Function	Description
$.Deferred([setupFunction])	Returns a new deferred object.
$.when(deferreds)	Returns a promise object to be resolved when the given deferred objects are resolved.

Methods of deferred objects

Method	Description
.resolve([args])	Sets the state of the object to resolved.
.resolveWith(context, [args])	Sets the state of the object to resolved while making the keyword this refer to context within callbacks.
.reject([args])	Sets the state of the object to rejected.
.rejectWith(context, [args])	Sets the state of the object to rejected while making the keyword this refer to context within callbacks.
.notify([args])	Executes any progress callbacks.
.notifyWith(context, [args])	Executes any progress callbacks while making the keyword this refer to context.
.promise([target])	Returns a promise object corresponding to this deferred object.

Methods of promise objects

Method	Description
.done(callback)	Executes callback when the object is resolved.
.fail(callback)	Executes callback when the object is rejected.
.always(callback)	Executes callback when the object is resolved or rejected.
.then(doneCallbacks, failCallbacks)	Executes doneCallbacks when the object is resolved, or failCallbacks when the object is rejected.
.progress(callback)	Executes callback each time the object receives a progress notification.
.isRejected()	Returns true if the object has been rejected.
.isResolved()	Returns true if the object has been resolved.
.state()	Returns 'pending', 'resolved', or 'rejected' depending on the current state.
.pipe([doneFilter], [failFilter])	Returns a new promise object which is resolved when the original promise is, optionally after filtering the object's status through a function.