Constate

Write local state using React Hooks and lift it up to React Context only when needed with minimum effort.

Basic example

``jsx
import React, { useState } from "react";
import constate from "constate";

// 1️⃣ Create a custom hook as usual
function useCounter() {
const [count, setCount] = useState(0);
const increment = () => setCount(prevCount => prevCount + 1);
return { count, increment };
}

// 2️⃣ Wrap your hook with the constate factory
const [CounterProvider, useCounterContext] = constate(useCounter);

function Button() {
// 3️⃣ Use context instead of custom hook
const { increment } = useCounterContext();
return +;
}

function Count() {
// 4️⃣ Use context in other components
const { count } = useCounterContext();
return {count};
}

function App() {
// 5️⃣ Wrap your components with Provider
return (




);
}
`

Learn more

Advanced example

`jsx
import React, { useState, useCallback } from "react";
import constate from "constate";

// 1️⃣ Create a custom hook that receives props
function useCounter({ initialCount = 0 }) {
const [count, setCount] = useState(initialCount);
// 2️⃣ Wrap your updaters with useCallback or use dispatch from useReducer
const increment = useCallback(() => setCount(prev => prev + 1), []);
return { count, increment };
}

// 3️⃣ Wrap your hook with the constate factory splitting the values
const [CounterProvider, useCount, useIncrement] = constate(
useCounter,
value => value.count, // becomes useCount
value => value.increment // becomes useIncrement
);

function Button() {
// 4️⃣ Use the updater context that will never trigger a re-render
const increment = useIncrement();
return

+;
}

function Count() {
// 5️⃣ Use the state context in other components
const count = useCount();
return {count};
}

function App() {
// 6️⃣ Wrap your components with Provider passing props to your hook
return (




);
}
`

Learn more

Installation

npm:

`sh
npm i constate
`

Yarn:

`sh
yarn add constate
`

API

$3

Constate exports a single factory method. As parameters, it receives useValue and optional selector functions. It returns a tuple of [Provider, ...hooks].

#### useValue

It's any custom hook:

`js
import { useState } from "react";
import constate from "constate";

const [CountProvider, useCountContext] = constate(() => {
const [count] = useState(0);
return count;
});
`

You can receive props in the custom hook function. They will be populated with :

`jsx
const [CountProvider, useCountContext] = constate(({ initialCount = 0 }) => {
const [count] = useState(initialCount);
return count;
});

function App() {
return (

...

);
}
`

The API of the containerized hook returns the same value(s) as the original, as long as it is a descendant of the Provider:

`jsx
function Count() {
const count = useCountContext();
console.log(count); // 10
}
`

#### selectors

Optionally, you can pass in one or more functions to split the custom hook value into multiple React Contexts. This is useful so you can avoid unnecessary re-renders on components that only depend on a part of the state.

A selector function receives the value returned by useValue and returns the value that will be held by that particular Context.

`jsx
import React, { useState, useCallback } from "react";
import constate from "constate";

function useCounter() {
const [count, setCount] = useState(0);
// increment's reference identity will never change
const increment = useCallback(() => setCount(prev => prev + 1), []);
return { count, increment };
}

const [Provider, useCount, useIncrement] = constate(
useCounter,
value => value.count, // becomes useCount
value => value.increment // becomes useIncrement
);

function Button() {
// since increment never changes, this will never trigger a re-render
const increment = useIncrement();
return

+;
}

function Count() {
const count = useCount();
return {count};
}
`

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` to run examples.

License

MIT © Diego Haz