Function batch

Batches multiple changes to stores while calling the provided function, preventing derived stores from updating until the function returns, to avoid unnecessary recomputations.

Remarks

If a store is updated multiple times in the provided function, existing subscribers of that store will only be called once when the provided function returns.

Note that even though the computation of derived stores is delayed in most cases, some computations of derived stores will still occur inside the function provided to batch if a new subscriber is added to a store, because calling subscribe always triggers a synchronous call of the subscriber and because tansu always provides up-to-date values when calling subscribers. Especially, calling get on a store will always return the correct up-to-date value and can trigger derived store intermediate computations, even inside batch.

It is possible to have nested calls of batch, in which case only the first (outer) call has an effect, inner calls only call the provided function.

Example

Using batch in the following example prevents logging the intermediate "Sherlock Lupin" value.

const firstName = writable('Arsène');
const lastName = writable('Lupin');
const fullName = derived([firstName, lastName], ([a, b]) => `${a} ${b}`);
fullName.subscribe((name) => console.log(name)); // logs any change to fullName
batch(() => {
    firstName.set('Sherlock');
    lastName.set('Holmes');
});
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