Constate
Write local state using React Hooks and lift it up to React Context only when needed with minimum effort.
Basic example
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 <button onClick={increment}>+</button>;
}
function Count() {
// 4️⃣ Use context in other components
const { count } = useCounterContext();
return <span>{count}</span>;
}
function App() {
// 5️⃣ Wrap your components with Provider
return (
<CounterProvider>
<Count />
<Button />
</CounterProvider>
);
}
Advanced example
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 <button onClick={increment}>+</button>;
}
function Count() {
// 5️⃣ Use the state context in other components
const count = useCount();
return <span>{count}</span>;
}
function App() {
// 6️⃣ Wrap your components with Provider passing props to your hook
return (
<CounterProvider initialCount={10}>
<Count />
<Button />
</CounterProvider>
);
}
Installation
npm:
npm i constate
Yarn:
yarn add constate
API
constate(useValue[, ...splitValues])
Constate exports a single factory method. As parameters, it receives useValue and multiple optional splitValue functions. It returns a tuple of [Provider, ...contextHooks].
useValue
It's any custom hook:
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 <Provider />:
const [CountProvider, useCountContext] = constate(({ initialCount = 0 }) => {
const [count] = useState(initialCount);
return count;
});
function App() {
return (
<CountProvider initialCount={10}>
...
</CountProvider>
);
}
The API of the containerized hook returns the same value(s) as the original, as long as it is a descendant of the Provider:
function Count() {
const count = useCountContext();
console.log(count); // 10
}
splitValues
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 splitValue function receives the value returned by useValue and returns the value that will be held by that particular Context.
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 <button onClick={increment}>+</button>;
}
function Count() {
const count = useCount();
return <span>{count}</span>;
}
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