Batching

batch(fn) is the store’s optional notifier buffer. Call it when a controller fires several back-to-back setState / replace / reset calls and you want subscribers to react once with the final state instead of after every intermediate update. State still mutates synchronously; batching simply defers the subscriber notification pass.

How it works

1. Entering batch increments an internal depth counter.
2. While depth > 0, updates mutate the store immediately but queue the store’s notifier instead of firing it. A Set dedupes multiple enqueues.
3. When the outermost batch exits, the queue flushes exactly once. Subscribers run a single notification pass no matter how many updates happened inside.
4. React receives that lone notification and re-checks selector values. Its own render batching rules still apply—batch just prevents the store from pinging subscribers hundreds of times.

How this differs from React’s batching

• React already collapses renders: if a selector yields new values mid-event, React still commits once with the final value.
• The cost is in notifications: every store.setState triggers a notify → snapshot read → compare loop. Without batching, you pay that loop for each update, even though React only renders once.
• Batching cuts the loop count: mutations still run synchronously, but subscribers are notified once at the end. That’s where the wall-time win comes from—fewer notification cycles, not different render semantics.
• Internal vs external: useState/useReducer updates invoked in React events are auto-batched by React. External stores notify React from the outside, so nothing coalesces them for you unless you use batch.

When to use it

• Normal app flows: call setState directly; batching is overkill.
• Multi-update bursts: wrap them in batch so controllers (optimistic updates, cross-slice coordination, benchmark loops) trigger one subscriber pass instead of many.
• Keep React’s own useState / useReducer calls outside batch; React already batches those internally.
• Plain store.getState() reads aren’t subscriptions, so batching has no effect on them.