A simple way to manage shared state in React

Built on the React Hooks API

Inspired by atoms in reagent.cljs

• Description
• Why use react-atom?
• Installation
• Documentation
• Code Example: react-atom in action
• 🕹️ Play with react-atom in CodeSandbox 🎮️
• Contributing / Feedback

Description

react-atom provides a very simple way to manage state in React, for both global app state and for local component state: ✨Atoms✨.

Put your state in an Atom:

import { Atom } from "@dbeining/react-atom";

const appState = Atom.of({
  color: "blue",
  userId: 1
});

Read state with deref

You can't inspect Atom state directly, you have to dereference it, like this:

import { deref } from "@dbeining/react-atom";

const { color } = deref(appState);

Update state with swap

You can't modify an Atom directly. The main way to update state is with swap. Here's its call signature:

function swap<S>(atom: Atom<S>, updateFn: (state: S) => S): void;

updateFn is applied to atom's state and the return value is set as atom's new state. There are just two simple rules for updateFn:

1. it must return a value of the same type/interface as the previous state
2. it must not mutate the previous state

To illustrate, here is how we might update appState's color:

import { swap } from "@dbeining/react-atom";

const setColor = color =>
  swap(appState, state => ({
    ...state,
    color: color
  }));

Take notice that our updateFn is spreading the old state onto a new object before overriding color. This is an easy way to obey the rules of updateFn.

Side-Effects? Just use swap

You don't need to do anything special for managing side-effects. Just write your IO-related logic as per usual, and call swap when you've got what you need. For example:

const saveColor = async color => {
  const { userId } = deref(appState);
  const theme = await post(`/api/user/${userId}/theme`, { color });
  swap(appState, state => ({ ...state, color: theme.color }));
};

Re-render components on state change with the ✨useAtom✨ custom React hook

useAtom is a custom React Hook. It does two things:

1. returns the current state of an atom (like deref), and
2. subscribes your component to the atom so that it re-renders every time its state changes

It looks like this:

export function ColorReporter(props) {
  const { color, userId } = useAtom(appState);

  return (
    <div>
      <p>
        User {userId} has selected {color}
      </p>
      {/* `useAtom` hook will trigger a re-render on `swap` */}
      <button onClick={() => swap(appState, setRandomColor)}>Change Color</button>
    </div>
  );
}

Nota Bene: You can also use a selector to subscribe to computed state by using the options.select argument. Read the docs for details.

Why use react-atom?

😌 Tiny API / learning curve

`Atom.of`, `useAtom`, and `swap` will cover the vast majority of use cases.

🚫 No boilerplate, just predictable state management

Reducers? Actions? Thunks? Sagas? Nope, just `swap(atom, state => newState)`.

🎵 Tuned for performant component rendering

The useAtom hook accepts an optional select function that lets components subscribe to computed state. That means the component will only re-render when the value returned from select changes.

😬 React.useState doesn't play nice with React.memo

useState is cool until you realize that in most cases it forces you to pass new function instances through props on every render because you usually need to wrap the setState function in another function. That makes it hard to take advantage of React.memo. For example:

---

function Awkwardddd(props) {
  const [name, setName] = useState("");
  const [bigState, setBigState] = useState({ ...useYourImagination });

  const updateName = evt => setName(evt.target.value);
  const handleDidComplete = val => setBigState({ ...bigState, inner: val });

  return (
    <>
      <input type="text" value={name} onChange={updateName} />
      <ExpensiveButMemoized data={bigState} onComplete={handleDidComplete} />
    </>
  );
}

Every time input fires onChange, ExpensiveButMemoized has to re-render because handleDidComplete is not strictly equal (===) to the last instance passed down.

The React docs admit this is awkward and suggest using Context to work around it, because the alternative is super convoluted.

With react-atom, this problem doesn't even exist. You can define your update functions outside the component so they are referentially stable across renders.

const state = Atom.of({ name, bigState: { ...useYourImagination } });

const updateName = ({ target }) => swap(state, prev => ({ ...prev, name: target.value }));

const handleDidComplete = val =>
  swap(state, prev => ({
    ...prev,
    bigState: { ...prev.bigState, inner: val }
  }));

function SoSmoooooth(props) {
  const { name, bigState } = useAtom(state);

  return (
    <>
      <input type="text" value={name} onChange={updateName} />
      <ExpensiveButMemoized data={bigState} onComplete={handleDidComplete} />
    </>
  );
}

TS First-class TypeScript support

react-atom is written in TypeScript so that every release is published with correct, high quality typings.

👣 Tiny footprint

⚛️ Embraces React's future with Hooks

Hooks will make class components and their kind (higher-order components, render-prop components, and function-as-child components) obsolete. react-atom makes it easy to manage shared state with just function components and hooks.

Installation

npm i -S @dbeining/react-atom

Dependencies

react-atom has one bundled dependency, @libre/atom, which provides the Atom data type. It is re-exported in its entirety from @dbeining/atom. You may want to reference the docs here.

react-atom also has two peerDependencies, namely, react@^16.8.0 and react-dom@^16.8.0, which contain the Hooks API.

Documentation

react-atom API

@libre/atom API

Code Example: react-atom in action

Click for code sample

import React from "react";
import ReactDOM from "react-dom";
import { Atom, useAtom, swap } from "@dbeining/react-atom";

//------------------------ APP STATE ------------------------------//

const stateAtom = Atom.of({
  count: 0,
  text: "",
  data: {
    // ...just imagine
  }
});

//------------------------ EFFECTS ------------------------------//

const increment = () =>
  swap(stateAtom, state => ({
    ...state,
    count: state.count + 1
  }));

const decrement = () =>
  swap(stateAtom, state => ({
    ...state,
    count: state.count - 1
  }));

const updateText = evt =>
  swap(stateAtom, state => ({
    ...state,
    text: evt.target.value
  }));

const loadSomething = () =>
  fetch("https://jsonplaceholder.typicode.com/todos/1")
    .then(res => res.json())
    .then(data => swap(stateAtom, state => ({ ...state, data })))
    .catch(console.error);

//------------------------ COMPONENT ------------------------------//

export const App = () => {
  const { count, data, text } = useAtom(stateAtom);

  return (
    <div>
      <p>Count: {count}</p>
      <p>Text: {text}</p>

      <button onClick={increment}>Moar</button>
      <button onClick={decrement}>Less</button>
      <button onClick={loadSomething}>Load Data</button>
      <input type="text" onChange={updateText} value={text} />

      <p>{JSON.stringify(data, null, "  ")}</p>
    </div>
  );
};

ReactDOM.render(<App />, document.getElementById("root"));

🕹️ Play with react-atom in CodeSandbox 🎮️

You can play with react-atom live right away with no setup at the following links:

JavaScript Sandbox	TypeScript Sandbox

Contributing / Feedback

Please open an issue if you have any questions, suggestions for improvements/features, or want to submit a PR for a bug-fix (please include tests if applicable).