2.0.0-beta.14: Proposal - Add affects() For Action-Affected Sources

[brenelz]

isPending(fn) is useful for checking whether a specific reactive read depends on pending async work, but it cannot currently distinguish or anticipate sources that an action is expected to update.

For example:

const user = createProjection(() => getUser(), {} as User)

const updateUser = action(function* (name: string) {
  yield updateUserServer(name)
  refresh(user)
})

In this case:

isPending(() => user.name)

only becomes true once refresh(user) starts. There is no way for the action to say "this source is affected by this mutation" earlier.

Proposed API

const updateUser = action(function* (name: string) {
  affects(user)

  yield updateUserServer(name)
})

Expected Behavior

• affects(user) marks user as pending for isPending() while the action is running.
• It does not mutate or refresh the source.
• It clears when the action settles.
• It should throw in dev mode if called outside an action.
• It should accept the same refreshable targets as refresh().

Example Usage

const pending = createMemo(() =>
  isPending(() => user.name)
)

const updateUser = action(function* (name: string) {
  affects(user)

  yield updateUserServer(name)
  refresh(user)
})

This lets UI show "saving/updating" state immediately for the affected source, instead of waiting for the later refresh.

[brenelz]

Yeah thinking about this a bit more its probably unneeded as you'd just use optimistic state. This would kind of be overloading what isPending means