Web/API/Window/unhandledrejection event

The unhandledrejection event is sent to the global scope of a script when a JavaScript Promise that has no rejection handler is rejected; typically, this is the window, but may also be a Worker. This is useful for debugging and for providing fallback error handling for unexpected situations.

Bubbles	No
Cancelable	Yes
Interface	`PromiseRejectionEvent`
Event handler property	`onunhandledrejection`

Usage notes

Allowing the unhandledrejection event to bubble will eventually result in an error message being output to the console. You can prevent this by calling preventDefault() on the PromiseRejectionEvent; see Preventing default handling below for an example.

Examples

Here we have a few examples showing ways you can make use of the unhandledrejection event. The event includes two useful pieces of information:

promise: The actual Promise which was rejected with no handler available to deal with the rejection.
reason: The reason that would have been passed into the rejection handler if one had existed. See catch() for details.

Basic error logging

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

window.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:

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

Preventing default handling

Many environments (such as [[../../../../Glossary/Node|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 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.

window.addEventListener('unhandledrejection', function (event) {
  // ...your code here to handle the unhandled rejection...

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

  event.preventDefault();
});

Specifications

Specification	Status	Comment
HTML Living StandardThe definition of 'unhandledrejection' in that specification.	Living Standard	Initial definition.

Browser compatibility

Update compatibility data on GitHub

	Desktop						Mobile
	Chrome	Edge	Firefox	Internet Explorer	Opera	Safari	Android webview	Chrome for Android	Firefox for Android	Opera for Android	Safari on iOS	Samsung Internet
`unhandledrejection` event	Chrome Full support 49	Edge Full support ≤79	Firefox Full support 69 Full support 69 Full support 68 Disabled' Disabled' From version 68: this feature is behind the `dom.promise_rejection_events.enabled` preference (needs to be set to `true`). To change preferences in Firefox, visit about:config.	IE No support No	Opera Full support 36	Safari Full support 11	WebView Android Full support 49	Chrome Android Full support 49	Firefox Android Full support 68 Disabled' Full support 68 Disabled' Disabled' From version 68: this feature is behind the `dom.promise_rejection_events.enabled` preference (needs to be set to `true`). To change preferences in Firefox, visit about:config.	Opera Android Full support 36	Safari iOS Full support 11.3	Samsung Internet Android Full support 5.0

Legend

Full support: Full support
No support: No support
User must explicitly enable this feature.': User must explicitly enable this feature.