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) {
console.log(e.reason);
} | Specification | Status | Comment |
|---|---|---|
| HTML Living Standard The definition of 'PromiseRejectionEvent.reason' in that specification. | Living Standard | Initial definition. |
| 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.
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https://developer.mozilla.org/en-US/docs/Web/API/PromiseRejectionEvent/reason