Constate

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

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import React, { useState } from "react";
import createUseContext 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 createUseContext factory
const useCounterContext = createUseContext(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 (
    <useCounterContext.Provider>
      <Count />
      <Button />
    </useCounterContext.Provider>
  );
}

Installation

npm:

npm i constate

Yarn:

yarn add constate

API

createUseContext(useValue[, createMemoInputs])

Constate exports a single factory method called createUseContext. It receives two arguments: useValue and createMemoInputs (optional). And returns a wrapped hook that can now read state from the Context. The hook also has two static properties: Provider and Context.

useValue

It's any custom hook:

import { useState } from "react";
import createUseContext from "constate";

const useCounterContext = createUseContext(() => {
  const [count] = useState(0);
  return count;
});

console.log(useCounterContext); // React Hook
console.log(useCounterContext.Provider); // React Provider
console.log(useCounterContext.Context); // React Context (if needed)

You can receive arguments in the custom hook function. They will be populated with <Provider />:

const useCounterContext = createUseContext(({ initialCount = 0 }) => {
  const [count] = useState(initialCount);
  return count;
});

function App() {
  return (
    <useCounterContext.Provider initialCount={10}>
      ...
    </useCounterContext.Provider>
  );
}

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 Counter() {
  const count = useCounterContext();
  console.log(count); // 10
}

createMemoInputs

Optionally, you can pass in a function that receives the value returned by useValue and returns an array of inputs. When any input changes, value gets re-evaluated, triggering a re-render on all consumers (components calling useContext()).

If createMemoInputs is undefined, it'll be re-evaluated everytime Provider renders:

// re-render consumers only when value.count changes
const useCounterContext = createUseContext(useCounter, value => [value.count]);

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

This works similarly to the inputs parameter in React.useEffect and other React built-in hooks. In fact, Constate passes it to React.useMemo inputs internally.

You can also achieve the same behavior within the custom hook. This is an equivalent implementation:

import { useMemo } from "react";

const useCounterContext = createUseContext(() => {
  const [count, setCount] = useState(0);
  const increment = () => setCount(count + 1);
  // same as passing `value => [value.count]` to `createMemoInputs` parameter
  return useMemo(() => ({ count, increment }), [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:start to run examples.

License

MIT © Diego Haz