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 errorDOMString
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
Specification | Status | Comment |
---|---|---|
HTML Living Standard The definition of 'PromiseRejectionEvent()' in that specification. |
Living Standard | Initial definition. |
Browser compatibility
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.