PromiseRejectionEvent: promise property

{{APIRef("HTML DOM")}}{{AvailableInWorkers}}

The {{domxref("PromiseRejectionEvent")}} interface's promise read-only property indicates the JavaScript {{jsxref("Promise")}} which was rejected. You can examine the event's {{domxref("PromiseRejectionEvent.reason")}} property to learn why the promise was rejected.

Value

The JavaScript {{jsxref("Promise")}} which was rejected, and whose rejection went unhandled.

Examples

This example listens for unhandled promises and, if the {{domxref("PromiseRejectionEvent.reason", "reason")}} is an object with a code field containing the text "Module not ready", it sets up an idle callback that will retry the task that failed to execute correctly.

{{domxref("event.preventDefault()")}} is called to indicate that the promise has now been handled.

window.onunhandledrejection = (event) => {
  if (event.reason?.code === "Module not ready") {
    requestIdleCallback((deadline) => {
      loadModule(event.reason.moduleName).then(performStartup);
    });
    event.preventDefault();
  }
};

Specifications

{{Specifications}}

Browser compatibility

{{Compat}}

See also

• Promise rejection events
• {{jsxref("Promise")}}
• {{domxref("PromiseRejectionEvent")}}
• {{domxref("Window.rejectionhandled_event", "rejectionhandled")}}
• {{domxref("Window.unhandledrejection_event", "unhandledrejection")}}