Zustand

When to Use Reducer vs Simple set

Use Reducer Pattern:

• Managing object lists/maps (messagesMap, topicMaps)
• Optimistic updates
• Complex state transitions

Use Simple set:

• Toggling booleans
• Updating simple values
• Setting single state fields

Optimistic Update Pattern

internal_createTopic: async (params) => {
  const tmpId = Date.now().toString();

  // 1. Immediately update frontend (optimistic)
  get().internal_dispatchTopic(
    { type: 'addTopic', value: { ...params, id: tmpId } },
    'internal_createTopic'
  );

  // 2. Call backend service
  const topicId = await topicService.createTopic(params);

  // 3. Refresh for consistency
  await get().refreshTopic();
  return topicId;
},

Delete operations: Don't use optimistic updates (destructive, complex recovery)

Naming Conventions

Actions:

• Public: createTopic, sendMessage

• Internal: internal_createTopic, internal_updateMessageContent

• Dispatch: internal_dispatchTopic State:

• ID arrays: topicEditingIds

• Maps: topicMaps, messagesMap

• Active: activeTopicId

• Init flags: topicsInit

Detailed Guides

• Action patterns: references/action-patterns.md
• Slice organization: references/slice-organization.md

Class-Based Action Implementation

We are migrating slices from plain StateCreator objects to class-based actions.

Pattern

• Define a class that encapsulates actions and receives (set, get, api) in the constructor.
• Use #private fields (e.g., #set, #get) to avoid leaking internals.
• Prefer shared typing helpers:
  • StoreSetter<T> from @/store/types for set.
  • Pick<ActionImpl, keyof ActionImpl> to expose only public methods.
• Export a create*Slice helper that returns a class instance.

type Setter = StoreSetter<HomeStore>;
export const createRecentSlice = (set: Setter, get: () => HomeStore, _api?: unknown) =>
  new RecentActionImpl(set, get, _api);

export class RecentActionImpl {
  readonly #get: () => HomeStore;
  readonly #set: Setter;

  constructor(set: Setter, get: () => HomeStore, _api?: unknown) {
    void _api;
    this.#set = set;
    this.#get = get;
  }

  useFetchRecentTopics = () => {
    // ...
  };
}

export type RecentAction = Pick<RecentActionImpl, keyof RecentActionImpl>;

Composition

• In store files, merge class instances with flattenActions (do not spread class instances).
• flattenActions binds methods to the original class instance and supports prototype methods and class fields.

const createStore: StateCreator<HomeStore, [['zustand/devtools', never]]> = (...params) => ({
  ...initialState,
  ...flattenActions<HomeStoreAction>([
    createRecentSlice(...params),
    createHomeInputSlice(...params),
  ]),
});

Multi-Class Slices

• For large slices that need multiple action classes, compose them in the slice entry using flattenActions.
• Use a local PublicActions<T> helper if you need to combine multiple classes and hide private fields.

type PublicActions<T> = { [K in keyof T]: T[K] };

export type ChatGroupAction = PublicActions<
  ChatGroupInternalAction & ChatGroupLifecycleAction & ChatGroupMemberAction & ChatGroupCurdAction
>;

export const chatGroupAction: StateCreator<
  ChatGroupStore,
  [['zustand/devtools', never]],
  [],
  ChatGroupAction
> = (...params) =>
  flattenActions<ChatGroupAction>([
    new ChatGroupInternalAction(...params),
    new ChatGroupLifecycleAction(...params),
    new ChatGroupMemberAction(...params),
    new ChatGroupCurdAction(...params),
  ]);

Store-Access Types

• For class methods that depend on actions in other classes, define explicit store augmentations:
  • ChatGroupStoreWithSwitchTopic for lifecycle switchTopic
  • ChatGroupStoreWithRefresh for member refresh
  • ChatGroupStoreWithInternal for curd internal_dispatchChatGroup

Do / Don't

• Do: keep constructor signature aligned with StateCreator params (set, get, api).
• Do: use #private to avoid set/get being exposed.
• Do: use flattenActions instead of spreading class instances.
• Don't: keep both old slice objects and class actions active at the same time.