The PromiseRejectionEvent.promise read-only property indicates the JavaScript Promise which has been rejected. You can examine the event's PromiseRejectionEvent.reason property to learn why the promise was rejected. Syntax promise = PromiseRejectionEvent.promise Specifications Specification Status Comment WHATWG HTML Living StandardThe definition of 'PromiseRejectionEvent.promise' in that specification. Living Standard Initial definition. Browser compatibility Desktop Mobile Feature Chrome Firefox (Gecko) Internet Explorer Opera Safari Basic support 49 No support No support No support No support Feature Android Firefox Mobile (Gecko) IE Mobile Opera Mobile Safari Mobile Basic support No support No support No support No support No support See also Promise PromiseRejectionEvent rejectionhandled unhandledrejection