# Constate
+ ;
}
function Count() {
// 4️⃣ Use context in other components
const { count } = useCounterContext();
return {count} ;
}
function App() {
// 5️⃣ Wrap your components with Provider
return (
);
}
```
[Learn more](#api)
## 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](#splitvalues)
## Installation
npm:
```sh
npm i constate
```
Yarn:
```sh
yarn add constate
```
## API
### `constate(useValue[, ...selectors])`
Constate exports a single factory method. As parameters, it receives [`useValue`](#usevalue) and optional [`selector`](#selectors) functions. It returns a tuple of `[Provider, ...hooks]`.
#### `useValue`
It's any [custom hook](https://reactjs.org/docs/hooks-custom.html):
```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 `
...
);
}
```
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`](#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](https://github.com/diegohaz/constate/issues/new) 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](https://github.com/diegohaz/constate/pulls).
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](https://akrabat.com/the-beginners-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](https://github.com/diegohaz)
Write local state using [React Hooks](https://reactjs.org/docs/hooks-intro.html) and lift it up to [React Context](https://reactjs.org/docs/context.html) only when needed with minimum effort.