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.


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

The actual Promise which was rejected with no handler available to deal with the rejection.
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 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



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

Browser compatibility

No compatibility data found. Please contribute data for "api.Window.unhandledrejection_event" (depth: 1) to the MDN compatibility data repository.

See also

[1] The corresponding event handler property is defined on the WindowEventHandlers mixin, which is available on both the Window interface and all types of Worker interfaces.

Document Tags and Contributors

Last updated by: wbamberg,