Scalable state manager using React Hooks & Context
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README.md

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Constate

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~ 1.5 kB React state management library that lets you write contextual state as if it were local state using React Hooks and React Context.


🕹 CodeSandbox demos 🕹
Counter I18n Theming TypeScript Wizard Form

import React from "react";
import { Provider, useContextState } from "constate";

// 1. Create a custom hook
function useCounter(key) {
  // 2. Replace React.useState(0) by useContextState(key, 0)
  const [count, setCount] = useContextState(key, 0);
  const increment = () => setCount(count + 1);
  return { count, increment };
}

function Count() {
  // 3. Consume the custom hook as usual
  const { count } = useCounter("counter1");
  return <span>{count}</span>
}

function IncrementButton() {
  // 4. Consume the same key in other components
  const { increment } = useCounter("counter1");
  return <button onClick={increment}>+</button>;
}

function App() {
  // 5. Wrap your app with Provider
  return (
    <Provider>
      <Count />
      <IncrementButton />
    </Provider>
  );
}

Table of Contents


Installation

npm:

npm i constate@next

Yarn:

yarn add constate@next

You'll need to install react@next and react-dom@next

Constate v1 is currently in early alpha. If you're looking for v0, see v0 docs or read the migration guide.


Provider

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First, you should wrap your app (or the part using Constate) with Provider so as to access contextual state within hooks:

import React from "react";
import { Provider } from "constate";

function App() {
  return (
    <Provider devtools={process.env.NODE_ENV === "development"}>
      ...
    </Provider>
  );
}

Passing devtools prop to Provider will enable the redux-devtools-extension integration, if that's installed in your browser. With that, you can easily debug the state of your application.

Using Redux Devtools Extension

Passing string to devtools prop will customize instance name shown on the monitor page

import React from "react";
import { Provider } from "constate";

function App() {
  return (
    <Provider devtools={process.env.NODE_ENV === "development" && 'App Store'}>
      ...
    </Provider>
  );
}

useContextState

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useContextState has the same API as React.useState, except that it receives contextKey as the first argument. It can be either a string or the return value of useContextKey.

All useContextState calls with the same contextKey throughout components in the Provider tree will share the same state.

import { useContextState } from "constate";

function Component() {
  // accesses state.contextKey in context
  const [state, setState] = useContextState("contextKey", "initialValue");
  ...
}

If you pass null or undefined into the contextKey parameter, it'll work exactly like React.useState:

import { useContextState } from "constate";

function Component() {
  // same as React.useState("initialValue")
  const [state, setState] = useContextState(null, "initialValue");
  ...
}

This means you can create custom hooks that can be either contextual or local depending on the component using it:

import React from "react";
import { useContextState } from "constate";

function useCounter(key) {
  const [count, setCount] = useContextState(key, 0);
  const increment = () => setCount(count + 1);
  return { count, increment };
}

function ContextualCounter() {
  const { count, increment } = useCounter("counter1");
  return <button onClick={increment}>{count}</button>;
}

function LocalCounter() {
  const { count, increment } = useCounter();
  return <button onClick={increment}>{count}</button>;
}

useContextReducer

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Just like useContextState, useContextReducer works similarly to React.useReducer, but accepting a contextKey argument, which can be either a string or the return value of useContextKey:

import { useContextReducer } from "constate";

function reducer(state, action) {
  switch(action.type) {
    case "INCREMENT": return state + 1;
    case "DECREMENT": return state - 1;
    default: return state;
  }
}

function useCounter(key) {
  const [count, dispatch] = useContextReducer(key, reducer, 0);
  const increment = () => dispatch({ type: "INCREMENT" });
  const decrement = () => dispatch({ type: "DECREMENT" });
  return { count, increment, decrement };
}

function ContextualCounter() {
  const { count, increment } = useCounter("counter1");
  return <button onClick={increment}>{count}</button>;
}

useContextKey

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Instead of passing strings to useContextState and useContextReducer, you can create a reference to the context key.

import { useContextKey } from "constate";

function Counter() {
  const key = useContextKey("counter1");
  const [count, setCount] = useContextState(key, 0);
  ...
}

It uses React.useRef underneath and is required when using useContextEffect.


useContextEffect

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Constate provides all contextual versions of React.useEffect, such as useContextEffect and useContextLayoutEffect.

They receive contextKey as the first argument. Unlike useContextState and useContextReducer, it's limited to the value returned by useContextKey. If contextKey is null or undefined, the hook will work exactly as the React one.

import { Provider, useContextKey, useContextEffect } from "constate";

let count = 0;

function useCounter(context) {
  // useContextKey is required for effects
  const key = useContextKey(context);
  useContextEffect(key, () => {
    count += 1;
  }, []);
}

function ContextualCounter1() {
  useCounter("counter1");
  ...
}

function ContextualCounter2() {
  useCounter("counter1");
  ...
}

function App() {
  return (
    <Provider>
      <ContextualCounter1 />
      <ContextualCounter2 />
    </Provider>
  );
}

In the example above, if we were using React.useEffect, count would be 2. With useContextEffect, it's 1.

useContextEffect ensures that the function will be called only once per contextKey no matter how many components are using it.


createContext

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If you want to set a initial state for the whole context tree and/or want to create separate contexts, you can use createContext:

// MyContext.js
import { createContext } from "constate";

const {
  Provider,
  useContextKey,
  useContextState,
  useContextReducer,
  useContextEffect,
  useContextLayoutEffect
} = createContext({
  counter1: 0,
  posts: [
    { id: 1, title: "Hello World!" }
  ]
});

export {
  Provider,
  useContextKey,
  useContextState,
  useContextReducer,
  useContextEffect,
  useContextLayoutEffect
};
// App.js
import React from "react";
import { Provider, useContextState } from "./MyContext";

function Counter() {
  // no need for initial value, it has been set in context
  const [count, setCount] = useContextState("counter1");
  const increment = () => setCount(count + 1);
  return <button onClick={increment}>{count}</button>;
}

function App() {
  return (
    <Provider>
      <Counter />
    </Provider>
  );
}

When importing hooks directly from the constate package, you're, in fact, using a default context created by our index file.


Contributing

If you find a bug, please create an issue providing instructions to reproduce it. It's always very appreciable if you find the time to fix it. In this case, please submit a PR.

If you're a beginner, it'll be a pleasure to help you contribute. You can start by reading the beginner's guide to contributing to a GitHub project.

When working on this codebase, please use yarn. Run yarn examples:start to run examples.


License

MIT © Diego Haz