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 rejectionhandled
event is emitted if a promise is rejected but the rejection is caught by a rejection handler.
promiseRejectionEvent = PromiseRejectionEvent(type, options);
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 should be one of rejectionhandled
or unhandledrejection
, to match the event names of the possible (non-synthetic) PromiseRejectionEvent
events that user agents can actually fire).
-
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.
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.
let myRejectionEvent = new PromiseRejectionEvent("unhandledrejection", {
promise : myPromise,
reason : "My house is on fire"
});