Reatom adapter for preact.

Installation

1npm i @reatom/preact

Read the handbook first for production usage.

Binding Atoms to Components

Reatom offers powerful ways to integrate state management directly into your Preact components, ensuring reactivity and proper lifecycle management.

reatomComponent

The primary API to bind atoms and actions to a component's lifetime is reatomComponent. It wraps your regular Preact component function, placing it within a Reatom reactive context.

Features:

• Reactive Reads: Simply call an atom (myAtom()) within the component function to read its value and subscribe to updates. The component will automatically re-render when the atom changes.
• Standard Preact: Use any other Preact hooks (useState, useEffect, etc.), accept props, and return any valid ReactNode as usual.
• Context Preservation: Event handlers should be wrapped with wrap() (e.g., onClick={wrap(myAction)}) to preserve the reactive context, especially for async operations or actions updating state.
• No Hooks Rules for Atoms: Call and subscribe to atoms conditionally within your render logic without violating Preact's rules of hooks.
• Automatic Cleanup: Integrates with Reatom's abort context. Effects or async operations triggered from within the component (using wrap or implicitly by actions) are automatically aborted if the component unmounts before completion, preventing race conditions and memory leaks.

1import { atom, wrap } from '@reatom/core'
2import { reatomComponent } from '@reatom/preact'
3
4export const page = atom(0, 'page').actions((target) => ({
5  next: () => target((state) => state + 1),
6  prev: () => target((state) => Math.max(0, state - 1)),
7}))
8
9// Simple component reading and updating global state
10export const Paging = reatomComponent(
11  () => (
12    <span>
13      <button onClick={wrap(page.prev)}>prev</button> {/* Use wrap */}
14      {page()} {/* Read atom value */}
15      <button onClick={wrap(page.next)}>next</button> {/* Use wrap */}
16    </span>
17  ),
18  'Paging',
19) // Naming the component is crucial for debugging!
20
21// Component accepting props (including atoms)
22type CounterProps = {
23  label: string
24  count: Atom<number>
25  increment: Action<[], number>
26}
27
28export const Counter = reatomComponent<CounterProps>(
29  ({ label, count, increment }) => (
30    <div>
31      {label}: {count()}
32      <button onClick={wrap(increment)}> + </button>
33    </div>
34  ),
35  'Counter',
36)
37
38// Conditional rendering based on atom values
39export const SomeList = reatomComponent(
40  () =>
41    isLoading() ? ( // Read atom conditionally
42      <span>Loading...</span>
43    ) : (
44      <ul>
45        {list().map(
46          (
47            el, // Read another atom
48          ) => (
49            <li key={el.id}>{el.text}</li>
50          ),
51        )}
52      </ul>
53    ),
54  'SomeList',
55)

Do not forget to put the component name to the second argument, it will increase your feature debug experience a lot!

Unmount Behavior

A key feature of reatomComponent is its integration with Reatom's abort mechanism. When a reatomComponent unmounts:

1. Its associated reactive context is aborted.
2. Any pending async operations initiated within that context (e.g., await wrap(fetch(...)), await wrap(sleep(...))) are automatically cancelled.
3. Any active effect primitives created within its context are automatically cleaned up.

This robust cleanup prevents common issues like trying to update state on unmounted components and avoids memory leaks from lingering subscriptions or timers. If you need an operation to survive component unmount (e.g., analytics), use spawn from the core package.

reatomFactoryComponent (Recommended for Local State/Effects)

While reatomComponent is great for reading atoms state, reatomFactoryComponent is the recommended pattern for components that need their own local, encapsulated state and side effects.

It separates the component logic into two parts:

1. Factory Function: Runs once when the component instance is created. This is where you define local atoms, actions, and effects specific to this component instance. It receives the component's initial props.
2. Render Function: Runs on every render, just like a regular Preact component function. It has access to the atoms and actions created in the factory scope and the current props.

Benefits:

• True Encapsulation: Local state and effects are tied to the component instance, not shared globally.
• Lifecycle Management: The factory scope provides a natural place for setup logic.
• Perfect for effect: effect primitives created in the factory are automatically cleaned up when the component unmounts, making it ideal for managing local subscriptions, timers, animations, etc.
• Stable References: Atoms, actions or any other functions created in the factory have stable references across renders.

1import { atom, action, effect, wrap, sleep } from '@reatom/core'
2import { reatomFactoryComponent } from '@reatom/preact'
3
4// Example: A self-contained counter component
5const Counter = reatomFactoryComponent<{ initialCount: number; step?: number }>(
6  // 1. Factory Function (runs once per instance)
7  (initProps) => {
8    // Note that the props will not change in this initialization scope.
9    const step = initProps.step ?? 1
10    // Create local atom specific to this Counter instance
11    const count = atom(initProps.initialCount, 'localCount')
12    // Create local action
13    const increment = action(() => count((c) => c + step), 'increment')
14    const decrement = action(() => count((c) => c - step), 'decrement')
15
16    // Example: Log changes (effect cleans up automatically)
17    effect(() => {
18      const currentCount = count()
19      console.log(`Counter ${initProps.initialCount} changed to:`, currentCount)
20      // Cleanup function (optional, runs before next effect run or on unmount)
21      return () =>
22        console.log(
23          `Counter ${initProps.initialCount} leaving state:`,
24          currentCount,
25        )
26    }, 'logEffect')
27
28    // Return the render function
29    return (props) => (
30      <div>
31        Count (Initial: {props.initialCount}, Step: {props.step ?? 1}):{' '}
32        {count()}
33        <button onClick={wrap(decrement)}>-</button>
34        <button onClick={wrap(increment)}>+</button>
35      </div>
36    )
37  },
38  'Counter', // Name the factory component!
39)
40
41// Usage:
42// <Counter initialCount={10} />
43// <Counter initialCount={0} step={5} />

Example: Using effect for Auto-Cleaning

reatomFactoryComponent combined with effect is excellent for managing resources that need cleanup. It is more powerful and precise primitive than useEffect, as it isn't coupled with rerenders.

1import { atom, effect, wrap, sleep, isAbort } from '@reatom/core'
2import { reatomFactoryComponent } from '@reatom/preact'
3
4const IntervalLogger = reatomFactoryComponent<{ intervalMs: number }>(
5  ({ intervalMs }) => {
6    const tick = atom(0, 'tick')
7
8    // This effect runs a timer and cleans it up automatically on unmount
9    effect(async () => {
10      while (true) {
11        // sleep respects the abort context
12        await wrap(sleep(intervalMs))
13        tick((t) => t + 1)
14      }
15    }, 'intervalEffect')
16
17    return (props) => (
18      <div>
19        Interval ({props.intervalMs}ms) Ticks: {tick()}
20      </div>
21    )
22  },
23  'IntervalLogger',
24)
25
26// Usage:
27// <IntervalLogger intervalMs={1000} />
28// When this component unmounts, the interval stops automatically.

reatomFactoryComponent provides a robust and elegant way to build stateful, effectful components with automatic lifecycle management, leveraging the power of Reatom's core primitives like atom and effect.

Setup context

Optionally, you need to set up the main context once and wrap your application in a provider at the top level. This is required if you have called clearStack() (recommended).

1import { context, connectLogger, clearStack } from '@reatom/core'
2import { reatomContext } from '@reatom/preact'
3import { Main } from './path/to/an/Main'
4
5// Recommended: Disable default context for predictability
6clearStack()
7
8const rootFrame = context.start()
9if (import.meta.env.DEV) {
10  rootFrame.run(connectLogger)
11}
12
13export const App = () => (
14  <reatomContext.Provider value={rootFrame}>
15    <Main />
16  </reatomContext.Provider>
17)