Version

3.2.23

Reproduction link

jsfiddle.net/ronzwj6g/

Steps to reproduce

1. Create a custom component
2. Apply a listener for a custom event (e.g. @custom="..." and @other="..." as per the example)
3. Observe how these are listed in $attrs of the component as $attrs.onCustom, $attrs.onOther etc.
4. Now implement the custom event by adding emits: ['custom'] to the custom component
5. Observe how $attrs.onCustom is now undefined
6. As a result, there appears to be no way to detect if a custom event listener is present on a component or not

What is expected?

For custom event listeners to show up in $attrs even if the component has them in its emits array.

What is actually happening?

The listener is undefined

Refer to https://stackoverflow.com/questions/46706737/check-if-a-component-has-an-event-listener-attached-to-it for more details on the use case etc.

they are missing just like declared props are missing from $attrs.

We have an open issue about this already where we noted that we might consider a way to access cust event listeners like you can access props. Can't find it right now though.

For now, you can declare the listener as a prop with on* prefix (which is how listeners are passed under the hood anyway), then you can check props.onCustom.

Alright thanks, if you can find the open issue so that I (or anyone finding this in the future) can track the progress for it that would be much appreciated.

I'm interested in this as well and I can't seem to find a related issue.

Duplicate of https://github.com/vuejs/vue-next/issues/4736#issuecomment-934212424