Unhandled promise rejections doesn't emit unhandledRejection event in the browser

[thomasguillory]

Using babel-polyfill, it seems I'm unable to catch promise rejections with this syntax:

window.addEventListener('unhandledRejection', (event) => {
   ...
})

However I'm able to catch them with

window.onunhandledrejection = (event) => {
   ...
}

I think it's related to this line:

core-js/library/modules/es6.promise.js

Line 116 in add384d

} else if(handler = global.onunhandledrejection){

[zloirock]

Yep, it still not implemented. I'll add it later. Feel free add a PR.

[alexbakerdev]

Hey, was just going to have a go implementing this, but didn't realise there is no polyfill for event/custom event for the reasons described here #354.

So not really sure how to resolve this.

Also it seems like maybe a large refactor to implement, here is my naive attempt with comments on why it wouldn't work:

      if(isUnhandled(promise)){
        if(isNode){
          process.emit('unhandledRejection', value, promise);
        } else {
          /**
          This is required to call onunhandledrejection on any browser except chrome
          but using in chrome this will cause it to be called twice as it
          will also be triggered when the event is dispatched on the window.
          */
          if(handler = global.onunhandledrejection){
            handler({promise: promise, reason: value});            
          }

          // This doesn't work in IE11-
          var unhandledRejectionEvent = new Event('unhandledrejection');

          unhandledRejectionEvent.promise = promise;
          unhandledRejectionEvent.reason = value;

          global.dispatchEvent(unhandledRejectionEvent)
        }

      // Also what condition should be used to determine logging like:
      // console.error('Unhandled promise rejection', value);
      } record.a = undefined;

I don't really have much experience with older browser quirks, so some help would be appreciated.

[Jessidhia]

You should be able to use document.createEvent('Event') in this case, despite being deprecated.

[zloirock]

Added to v3 branch.