useId return type is potentially undefined

[jack-allocate]

Vue version

3.5.4

Link to minimal reproduction

https://play.vuejs.org/#eNp9kEFLAzEQhf9KyKUKZT2ol9oKKj3Ug4p6DMiSna6p2SQkk3VhyX93kqW1gvSybN73MvPyRn7nXNVH4Au+DNIrhywARsd0bdqV4BgEvxVGdc56ZCOLATYNS2zrbcdmdHEmjDDSmoAMgT6ryXJ2fiPM8mIaSQPogNA5XSPQibFxzO6UsukI8DltpGlb1Va7YA3FGrNdcGk7pzT4Z4eKtgm+YIVkVmttvx+Lhj7CfK/LT5Bf/+i7MGRN8BcPAXwPgh8Y1r4FnPD67QkG+j/AzjZRk/sEfIVgdcwZJ9t9NA3FPvKVtJtSqDLte1gPCCbsH/UnaECvZAmT5aymwgSn5h9ONPL7isvqutwTJlG5Hz34vIp6JVBd8fQDoa+puA==

Steps to reproduce

Hover over id to see the type

What is expected?

Return type is string

What is actually happening?

Return type is string | undefined

System Info

No response

Any additional comments?

No response

[JohnieXu]

that's right, it should be string | undefined

core/packages/runtime-core/src/helpers/useId.ts

Lines 7 to 17 in d0b513e

	export function useId(): string | undefined {
	const i = getCurrentInstance()
	if (i) {
	return (i.appContext.config.idPrefix || 'v') + '-' + i.ids[0] + i.ids[1]++
	} else if (__DEV__) {
	warn(
	`useId() is called when there is no active component ` +
	`instance to be associated with.`,
	)
	}
	}

[andrey-hohlov]

Does anyone else finds it annoying to always cast it to string?

const id = useId() as string;

[sgoess]

I have also encountered this issue today. It's new to me that the return type of useId can be undefined, as this is not documented in the Vue documentation: https://vuejs.org/api/composition-api-helpers#useid

There is also some discussion about this here: #11404

I'm not sure how to handle an undefined value in this context. It would be very helpful if the documentation could be updated to reflect this behavior, along with some guidance on how to manage the possibility of undefined.

Thanks!

[edison1105]

const id = useId()!

[yyx990803]

After thinking about this, we do already have other helpers like useAttrs() and useTemplateRef() that return a non-nullable type even when there is no active instance, and I think we should keep useId() consistent with that (i.e. always return a string). See a177092