PromiseRejectionEvent.constructor

The PromiseRejectionEvent() constructor returns a newly created PromiseRejectionEvent, which represents events fired when a JavaScript Promise is rejected. With promise rejection events, it becomes possible to detect and report promises which fail and whose failures go unnoticed. It also becomes easier to write a global handler for errors.

There are two types of PromiseRejectionEvent: unhandledrejection is sent by the JavaScript runtime when a promise is rejected but the rejection goes unhandled. A recipient of unhandledrejection sends a rejectionhandled event if it handles the rejection, so the system knows to stop treating the rejection as unhandled.

Syntax

PromiseRejectionEvent = PromiseRejectionEvent(type, options);

Parameters

The PromiseRejectionEvent() constructor also inherits parameters from Event().

type

A string representing the name of the type of the PromiseRejectionEvent. This is case-sensitive and must be one of "rejectionhandled" or "unhandledrejection".

options

An Object specifying details about the rejection which occurred:

promise

The Promise that was rejected.

reason

Any value or Object which represents the reason the promise was rejected. This can be anything from a numeric error code to an error DOMString to an object which contains detailed information describing the situation resulting in the promise being rejected.

Return value

A new PromiseRejectionEvent configured as specified by the parameters.

Examples

This example creates a new unhandledrejection event for the promise myPromise with the reason being the string "My house is on fire". The reason could just as easily be a number, or even an object with detailed information including the home address, how serious the fire is, and the phone number of an emergency contact who should be notified.

var myRejectionEvent = new PromiseRejectionEvent('unhandledrejection', {
  promise : myPromise,
  reason : 'My house is on fire'
});

Specifications

Browser compatibility

[1] Firefox implements the PromiseRejectionEvent interface if you go to about:config and set the dom.promise_rejection_events.enabled pref to true. However, Firefox doesn't yet actually send the unhandledrejection or understand rejectionhandled events. Completing the implementation will be addressed in bug 1362272.

See also

• Promise
• PromiseRejectionEvent