batch

batch runs several writes and delivers every notification they caused once, afterwards, in order.

Import

import { batch } from '@bedrock-core/observable';

Signature

batch(fn: () => void): void

Parameters

Parameter	Type	Default	Description
fn *	() => void	—	The writes to group; runs immediately

Returns

Nothing. Every listener the writes affected has run by the time batch returns.

Usage

const phase = observable('fight');
const alive = observable(new Set(['steve', 'alex']));

batch(() => {
  phase.set('end');
  alive.set(new Set());
});
// phase's listeners ran once with ('end', 'fight'); alive's ran once

Examples

A value that changes and changes back

batch(() => {
  volume.set(0);
  volume.set(50);   // back to what listeners last saw
});
// nobody is notified

A computed over two changed inputs

const total = computed(() => price.get() * quantity.get(), [price, quantity]);

batch(() => {
  price.set(10);
  quantity.set(3);
});
// total recomputed once, from (10, 3)

Notes

• Nested batches flush at the outermost. A batch inside a batch is part of the outer one.
• Order is preserved. Notifications are delivered in the order the observables were first written.
• A flush is itself a batching window. A listener that sets another observable during delivery queues it behind the current one instead of interleaving, and it is delivered in the same synchronous pass.
• Outside a batch, delivery is synchronous inside set; batch is the only thing that defers.