Why is the return type of useWatch a deep partial unlike the one from useFormContext's watch?

[Zetxus]

Using useWatch<T>() (parameterless) makes my entire codebase have to either cast the result to the non-partial value (T) or @ts-ignore the type in order to get my defined type instead of the deep partial one.

The watch type from the useFormContext is unchanged but that always results in infinite updates when I try to use it the same way I use useWatch and gives me performance issues so I've moved away from using it even though the typing there is what I need.

[delyan-peev]

+1, this is a peculiar case we've been repeatedly fighting in similar ways amongst our codebase

[Zetxus]

@bluebill1049 @Moshyfawn

Sorry to tag you like this but I really didn't want to open an issue in order to get your attention and I'm pretty sure you guys are the only ones who could answer this well.

[leapful]

@Zetxus

Please provide a codesandbox url to describe more details on your issue. The example from react-hook-form https://codesandbox.io/s/react-hook-form-v7-ts-usewatch-forked-g399v7 shows correct type without casting or ignore anything.

[delyan-peev]

OP explicitly mentioned parameterless. I think that's what he meant:

https://codesandbox.io/s/react-hook-form-v7-ts-usewatch-forked-mykjmc?file=/src/index.tsx

Check the different returned types from useWatch() and watch()

P.S. What's strange to me is that in the case you showed where you useWatch a field by name, the return type is correct, but when used without parameters (useWatching the whole form), the return type is a DeepPartial. There is a possible workaround where you place the whole form inside of a root-level field (e.g. data) and then use useWatch({ name: 'data' }) but it seems a bit hacky. Currently, we are having trouble finding a way to leverage the efficiency of useWatch when you need to watch the whole form.

[Zetxus]

That's exactly what I meant, my bad for neglecting to provide an example. The provided example displays what I'm experiencing as well.

[Zetxus]

@leapful any insights on this?

[leapful]

@Zetxus @delyan-peev

I think it was caused by different type definition of parameterless useWatch() and watch(), one is using deep partial, the other does not. The reason is because useWatch hook also supports parameter defaultValue so it must be deep partial to match the context value.

Could you please open an issue for this improvement ? Feel free to open a related pull request for this case. Thank you :D

[Zetxus]

Sorry we've been crunching for the past few weeks so I just managed to get around to do this. I opened an issue linking to this discussion. If I manage to clear some time I'll try to familiarize myself with the code and open a PR, but I'm not optimistic about my timetable right now.

[glenjamin]

I just ran into this too - there was an open issue describing the problem in #9919 - but it was closed as resolved despite not being resolved - was that intentional?