Better JSX types for form events

[henribru]

What problem does this feature solve?

Currently the JSX types specify that native input event handlers receive an Event: https://github.com/vuejs/vue-next/blob/8ed3ed6c27b0fb9a1b6994eddc967e42d4b3d4e1/packages/runtime-dom/types/jsx.d.ts#L1210

This is very general compared to the runtime type. As an example, @input on an input element will actually give you an InputEvent. It would be useful if the correct event type could be inferred so that we don't have to cast the event object. I assume it's not as simple as e.g. replacing Event with InputEvent for onInput or it would probably have been done already, but is this something that could potentially be solved?

What does the proposed API look like?

N/A, just a type improvement, not an API

[pikax]

I was thinking we could have something similar to what React does #3370

[ctrlplusb]

Would love this. I have had to write a utility to narrow the event types at the moment but would prefer to avoid the additional boilerplate.

[kidonng]

I assume it's not as simple as e.g. replacing Event with InputEvent for onInput or it would probably have been done already

Would like an explanation why they are typed as such. They are only used for JSX so I don't think it would actually break anything.

@pikax kindly asking what's blocking #3370? If that PR could not be landed in the near future, could we at least have these types corrected (e.g. onInput: InputEvent) first?

[kleinfreund]

#9675 fixes the incorrect type definitions which seems to be the more immediately relevant fix. I'm running into this issue when assigning submit event listeners to form elements and using event: SubmitEvent in the listener's signature.