@preact/signals-react

Signals

Signals is a performant state management library with two primary goals:

1. Make it as easy as possible to write business logic for small up to complex apps. No matter how complex your logic is, your app updates should stay fast without you needing to think about it. Signals automatically optimize state updates behind the scenes to trigger the fewest updates necessary. They are lazy by default and automatically skip signals that no one listens to.
2. Integrate into frameworks as if they were native built-in primitives. You don't need any selectors, wrapper functions, or anything else. Signals can be accessed directly and your component will automatically re-render when the signal's value changes.

Read the announcement post to learn more about which problems signals solves and how it came to be.

Installation:

npm install @preact/signals-react

• Guide / API
  • signal(initialValue)
    • signal.peek()
  • computed(fn)
  • effect(fn)
  • batch(fn)
  • untracked(fn)
• React Integration
  • Hooks
• License

React Integration

Note: The React integration plugs into some React internals and may break unexpectedly in future versions of React. If you are using Signals with React and encounter errors such as "Rendered more hooks than during previous render", "Should have a queue. This is likely a bug in React." or "Cannot redefine property: createElement" please open an issue here.

The React integration can be installed via:

npm install @preact/signals-react

Similar to the Preact integration, the React adapter allows you to access signals directly inside your components and will automatically subscribe to them.

import { signal } from "@preact/signals-react";

const count = signal(0);

function CounterValue() {
	// Whenever the `count` signal is updated, we'll
	// re-render this component automatically for you
	return <p>Value: {count.value}</p>;
}

Hooks

If you need to instantiate new signals inside your components, you can use the useSignal or useComputed hook.

import { useSignal, useComputed } from "@preact/signals-react";

function Counter() {
	const count = useSignal(0);
	const double = useComputed(() => count.value * 2);

	return (
		<button onClick={() => count.value++}>
			Value: {count.value}, value x 2 = {double.value}
		</button>
	);
}

Rendering optimizations

The React adapter ships with several optimizations it can apply out of the box to skip virtual-dom rendering entirely. If you pass a signal directly into JSX, it will bind directly to the DOM Text node that is created and update that whenever the signal changes.

import { signal } from "@preact/signals-react";

const count = signal(0);

// Unoptimized: Will trigger the surrounding
// component to re-render
function Counter() {
	return <p>Value: {count.value}</p>;
}

// Optimized: Will update the text node directly
function Counter() {
	return (
		<p>
			<>Value: {count}</>
		</p>
	);
}

To opt into this optimization, simply pass the signal directly instead of accessing the .value property.

Note The content is wrapped in a React Fragment due to React 18's newer, more strict children types.

License

MIT, see the LICENSE file.