Why do we need batching in signals if React batches state updates?

[crabvk]

Just stumbled upon the batch function in the guide which led to the question.

[rschristian]

React can batch state updates, but there's no guarantees how or when they will. batch() provides this guarantee.

import { signal, computed, effect } from '@preact/signals-react';

const fName = signal('John');
const lName = signal('Smith');
const fullName = computed(() => `${fName.value} ${lName.value}`);

effect(() => console.log(fullName.value));

fName.value = 'Jane';
lName.value = 'Doe';

This could log:

John Smith
Jane Smith
Jane Doe

Batching the name updates will always log this:

John Smith
Jane Doe

[rschristian]

Of course, signals also integrate into Preact and are also provided as UI framework-agnostic core library, React's behavior is just a piece of the whole.