Window: rejectionhandled event

The rejectionhandled event is sent to the script's global scope (usually window but also Worker) whenever a rejected JavaScript Promise is handled late, i.e., when a handler is attached to the promise after its rejection had caused an unhandledrejection event.

This can be used in debugging and for general application resiliency, in tandem with the unhandledrejection event, which is sent when a promise is rejected but there is no handler for the rejection at the time.

Syntax

Use the event name in methods like addEventListener(), or set an event handler property.

addEventListener("rejectionhandled", (event) => { })

onrejectionhandled = (event) => { }

Event type

A PromiseRejectionEvent. Inherits from Event.

Event properties

PromiseRejectionEvent.promise Read only: The JavaScript Promise that was rejected.
PromiseRejectionEvent.reason Read only: A value or Object indicating why the promise was rejected, as passed to Promise.reject().

Event handler aliases

In addition to the Window interface, the event handler property onrejectionhandled is also available on the following targets:

Example

You can use the rejectionhandled event to log promises that get rejected to the console, along with the reasons why they were rejected:

window.addEventListener(
  "rejectionhandled",
  (event) => {
    console.log(`Promise rejected; reason: ${event.reason}`);
  },
  false,
);

Specifications

Specification
HTML # unhandled-promise-rejections
HTML # handler-window-onrejectionhandled