The PromiseRejectionEvent.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


window.onunhandledrejection = function(e) {


Specification Status Comment
WHATWG HTML Living Standard
The definition of 'PromiseRejectionEvent.reason' 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] In Firefox, this is implemented but disabled by default. To turn it on, go to about:config and set the dom.promise_rejection_events.enabled pref to true.

See also

Document Tags and Contributors

 Contributors to this page: chrisdavidmills, fscholz, Sheppy
 Last updated by: chrisdavidmills,