WorkerGlobalScope: unhandledrejection event

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

The unhandledrejection event is sent to the global scope (typically {{domxref("WorkerGlobalScope")}}) of a script when a {{jsxref("Promise")}} that has no rejection handler is rejected.

This is useful for debugging and for providing fallback error handling for unexpected situations.

Syntax

Use the event name in methods like {{domxref("EventTarget.addEventListener", "addEventListener()")}}, or set an event handler property.

addEventListener("unhandledrejection", (event) => { })

onunhandledrejection = (event) => { }

Event type

A {{domxref("PromiseRejectionEvent")}}. Inherits from {{domxref("Event")}}.

{{InheritanceDiagram("PromiseRejectionEvent")}}

Event properties

• {{domxref("PromiseRejectionEvent.promise")}} {{ReadOnlyInline}}
  • : The JavaScript {{jsxref("Promise")}} that was rejected.
• {{domxref("PromiseRejectionEvent.reason")}} {{ReadOnlyInline}}
  • : A value or {{jsxref("Object")}} indicating why the promise was rejected, as passed to {{jsxref("Promise.reject()")}}.

Examples

Basic error logging

This example logs information about the unhandled promise rejection to the console.

self.addEventListener("unhandledrejection", (event) => {
  console.warn(`UNHANDLED PROMISE REJECTION: ${event.reason}`);
});

You can also use the onunhandledrejection event handler property to set up the event listener:

self.onunhandledrejection = (event) => {
  console.warn(`UNHANDLED PROMISE REJECTION: ${event.reason}`);
};

Preventing default handling

Many environments (such as {{Glossary("Node.js")}}) report unhandled promise rejections to the console by default. You can prevent that from happening by adding a handler for unhandledrejection events that—in addition to any other tasks you wish to perform—calls {{domxref("Event.preventDefault()", "preventDefault()")}} to cancel the event, preventing it from bubbling up to be handled by the runtime's logging code. This works because unhandledrejection is cancelable.

self.addEventListener("unhandledrejection", (event) => {
  // code for handling the unhandled rejection
  // …

  // Prevent the default handling (such as outputting the
  // error to the console)

  event.preventDefault();
});

Specifications

{{Specifications}}

Browser compatibility

{{Compat}}

See also

• Promise rejection events
• {{domxref("PromiseRejectionEvent")}}
• {{jsxref("Promise")}}
• {{domxref("WorkerGlobalScope/rejectionhandled_event", "rejectionhandled")}} event