loadable atom doesn't have type for returned value data and error properties

[trongthanh]

Bug Description

Jotai 2.9.3

The returned value from a useAtom(loadableAtom) only has type definition for state. And no type inference for the data property based on the async atom. Besides, error doesn't exist as a property.

Reproduction Link

https://stackblitz.com/edit/jotai-gmwmbz?file=src%2FApp.tsx

[dai-shi]

You can check the state and then access it.
https://stackblitz.com/edit/jotai-gmwmbz-lfvpq2?file=src%2FApp.tsx

[thanhtran-ct]

Of course I can write check routine to make sure data is defined. My bug (or feature request) is that can the loadable atom infer the returned type of the wrapped async atom and report the type of data property as union with undefined? For example, in this case, data property should exist with type string | undefined?

For the error property, it is fine as is. User can check and cast the type case by case

[dai-shi]

jotai/src/vanilla/utils/loadable.ts

Lines 17 to 20 in 9b83585

	export type Loadable<Value> =
	| { state: 'loading' }
	| { state: 'hasError'; error: unknown }
	| { state: 'hasData'; data: Awaited<Value> }

is the type we are using. We generally avoid adding | undefined in all Jotai code base. So, your request is not acceptable.

If you want to loosen the type, you can work it around with type assertion:
https://stackblitz.com/edit/jotai-gmwmbz-rbdn9a?file=src%2FApp.tsx
It's not very cute though.

[trongthanh]

Agree, type assertion at userland is counterproductive of type convenience. However, as I'm writing a wrapper around loadable so this is acceptable for now.