The Window.onrejectionhandled property is an event handler for processing rejectionhandled events, which are raised when Promises are rejected. Syntax window.addEventListener("rejectionhandled", function(event) { ... }); window.onrejectionhandled = function(event) { ...}; Specifications Specification Status Comment WHATWG HTML Living StandardThe definition of 'onrejectionhandled' in that specification. Living Standard Initial definition. Browser compatibility Desktop Mobile Feature Chrome Firefox (Gecko) Internet Explorer Opera Safari (WebKit) Basic support 49 ? ? ? ? Feature Android Android Webview Firefox Mobile (Gecko) Firefox OS IE Mobile Opera Mobile Safari Mobile Chrome for Android Basic support No support No support ? ? ? ? ? No support