Alex Rickabaugh 906413aba3 fix(core): change Resource to use explicit undefined in its typings (#59024) ...

Originally the `T` in `Resource<T>` represented the resolved type of the
resource, and `undefined` was explicitly added to this type in the `.value`
signal. This turned out to be problematic, as it wasn't possible to write a
type for a resource which didn't return `undefined` values. Such a type is
useful for 2 reasons:

1. to support narrowing of the resource type when `Resource.hasValue()`
   returns `true`.

2. for resources which use a different value instead of `undefined` to
   represent not having a value (for example, array resources which want to
   use `[]` as their default).

Instead, this commit changes `resource()` and `rxResource()` to return an
explicit `ResourceRef<T|undefined>`, and removes the union with `undefined`
from all types related to the resource's value. This way, it's trivially
possible to write `Resource<T>` to represent resources where `.value` only
returns `T`.

`hasValue()` then actually works to perform narrowing, by narrowing the
resource type to `Exclude<T, undefined>`.

PR Close #59024

2025-01-16 09:22:46 -08:00

..

index.api.md

fix(core): change Resource to use explicit undefined in its typings (#59024)

2025-01-16 09:22:46 -08:00