The read-only PromiseRejection property reason read-only property is any JavaScript value or Object which provides the reason passed into Promise.reject(). This in theory provides information about why the promise was rejected.


reason = PromiseRejectionEvent.reason


A  value or object which provides information you can use to understand why the promise was rejected. This could be anything from an error code to an object with text, links, and whatever else you might wish to include.


window.onunhandledrejection = function(e) {


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

Browser compatibility

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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,