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.


PromiseRejectionEvent = PromiseRejectionEvent(type, options);


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

A string representing the name of the type of the PromiseRejectionEvent. This is case-sensitive and must be one of "rejectionhandled" or "unhandledrejection".
An Object specifying details about the rejection which occurred:
The Promise that was rejected.
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.


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'


Specification Status Comment
HTML Living Standard
The definition of 'PromiseRejectionEvent()' in that specification.
Living Standard Initial definition.

Browser compatibility

We're converting our compatibility data into a machine-readable JSON format. This compatibility table still uses the old format, because we haven't yet converted the data it contains. Find out how you can help!

Feature Chrome Firefox (Gecko) Internet Explorer Opera Safari
Basic support 49 No support[1] No support No support No support
Feature Android Firefox Mobile (Gecko) IE Mobile Opera Mobile Safari Mobile
Basic support No support No support[1] No support No support No support

[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

Document Tags and Contributors

Contributors to this page: Sheppy, chrisdavidmills, fscholz
Last updated by: Sheppy,