WinJS.Promise object

Provides a mechanism to schedule work to be done on a value that has not yet been computed. It is an abstraction for managing interactions with asynchronous APIs.

For more information about asynchronous programming, see Asynchronous programming. For more information about promises in JavaScript, see Asynchronous programming in JavaScript.

Syntax

var aPromise = new WinJS.Promise(init, onCancel);

Members

The Promise object has these types of members:

• Constructors
• Events
• Methods

Constructors

The Promise object has these constructors.

Constructor	Description
Promise	A promise provides a mechanism to schedule work to be done on a value that has not yet been computed. It is a convenient abstraction for managing interactions with asynchronous APIs. For more information about asynchronous programming, see Asynchronous programming. For more information about promises in JavaScript, see Asynchronous programming in JavaScript.

 

Events

The Promise object has these events.

Event	Description
onerror	Occurs when there is an error in processing a promise.

 

Methods

The Promise object has these methods.

Method	Description
addEventListener	Adds an event listener for the promise.
cancel	Attempts to cancel the fulfillment of a promised value. If the promise hasn't already been fulfilled and cancellation is supported, the promise enters the error state with a value of Error("Canceled").
dispatchEvent	Raises an event of the specified type and properties.
done	Allows you to specify the work to be done on the fulfillment of the promised value, the error handling to be performed if the promise fails to fulfill a value, and the handling of progress notifications along the way. After the handlers have finished executing, this function throws any error that would have been returned from then as a promise in the error state. For more information about the differences between then and done, see the following topics: Quickstart: using promises in JavaScript How to handle errors when using promises in JavaScript Chaining promises in JavaScript
removeEventListener	Removes an event listener from the control.
then	Allows you to specify the work to be done on the fulfillment of the promised value, the error handling to be performed if the promise fails to fulfill a value, and the handling of progress notifications along the way. For more information about the differences between then and done, see the following topics: Quickstart: using promises in JavaScript How to handle errors when using promises in JavaScript Chaining promises in JavaScript

 

Requirements

Minimum WinJS version	WinJS 2.0
Namespace	WinJS