The PromiseRejectionEvent interface's promise read-only property indicates the JavaScript Promise which was rejected. You can examine the event's PromiseRejectionEvent.reason property to learn why the promise was rejected.


promise = PromiseRejectionEvent.promise


The JavaScript Promise which was rejected, and whose rejection went unhandled.


This example listens for unhandled promises and, if the reason is an object with a code field containing the text "Module not ready", it sets up an idle callback that will retry the task that failed to execute correctly.

event.preventDefault() is called to indicate that the promise has now been handled.

window.onunhandledrejection = function(event) {
  if (event.reason.code && event.reason.code == "Module not ready") {
    window.requestIdleCallback(function(deadline) {


Specification Status Comment
HTML Living Standard
The definition of 'PromiseRejectionEvent.promise' 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,