Core concepts

A store is defined by three optional-but-typed parts.

State

The initial state object. Its shape is inferred everywhere.

state: { count: 0, user: null as User | null }

Actions

Pure functions: they receive the current state (plus any args) and return a partial that is shallow-merged in.

actions: {
  increment: (s) => ({ count: s.count + 1 }),
  add: (s, n: number) => ({ count: s.count + n }),
}

The bound action drops the state parameter, so you call add(5).

Computed

Derived values, recomputed from state on every change.

computed: {
  doubled: (s) => s.count * 2,
  isEven: (s) => s.count % 2 === 0,
}

One namespace

State, computed, and action names are merged into one object, so they must be unique. A duplicate key throws when the store is created.