usestate-memoize

memoize/cache solution for React useState

This package uses React.useState and React.useState for cache solution.

What's the "problem" with React.useState

What happen in a code like this one?

import React, { memo, useState } from 'react';

const MyCounter = memo(() => {
	const [ count, setCount ] = useState(0);

	return <>
		<Button onClick={() => setCount(count+1)}>Increment me!</Button>
		<Button onClick={() => setCount(count-1)}>Decrement me!</Button>
		<span>Value is {count}</span>
	</>
});

const Button = memo(({onClick, children}) => {
	console.log("I'm rendered!");
	return (
		<Button onClick={onClick}>{children}</Button>
	);
});

Each time you click a button, Component is re-rendered, and onClick function references are changed (because you create a new function at each render). While this change of references are pretty insignificant Are hooks slow because of creating functions in render?, when we have multiple components, with many componentDidUpdate or useEffects logics, it would be better not to recreate functions each time, and causing children to re-render

Installation

npm i usestate-memoize

Usage

import React, { memo } from 'react';
import useState from 'usestate-memoize';

const _inc = () => c => c+1;
const _dec = () => c => c-1;
const MyCounter = memo(() => {
	const [ count, setCount, defineCountActions, actions ] = useState(0, {
		increment: _inc,
		decrement: _dec,
	});

	return <>
		<Button onClick={actions.increment}>Increment me!</Button>
		<Button onClick={actions.decrement}>Decrement me!</Button>
		<span>Value is {count}</span>
	</>
});

const Button = memo(({onClick, children}) => {
	console.log("I'm rendered!");
	return (
		<Button onClick={onClick}>{children}</Button>
	);
})

usestate-memoize exposes same api as React.useState. It returns a 4 values array:

[0] State value (same as React.useState)

[1] Function to set state value(same as React.useState)

[2] Function to bind a custom function which will be memoized

[3] Shortcut to access auto-memoized functions defined in useState constructor

const _inc = () => c => c+1;
const _dec = () => c => c-1;
const MyCounter = () => {
    const [ count, setCount, defineCountActions] = useState(0);

	const increment = defineCountActions(_inc);
	const decrement = defineCountActions(_dec);

    return <>
        <Button onClick={increment}>Increment me!</Button>
        <Button onClick={decrement}>Decrement me!</Button>
        <span>Value is {count}</span>
    </>
};

Note that _inc and _dec are defined OUTSIDE of component. If you define these functions inside your functional component, they will be re-created each-time, and you'll loose memoization.

usestate-memoized provides a shortcut, to auto-memoized custom actions, passing them in constructor, and getting back them as fourth array value

const _inc = () => c => c+1;
const _dec = () => c => c-1;
const MyCounter = () => {
    const [ count,,, { increment, decrement } ] = useState(0, {
		increment: _inc,
		decrement: _dec,
	});

    return <>
        <Button onClick={increment}>Increment me!</Button>
        <Button onClick={decrement}>Decrement me!</Button>
        <span>Value is {count}</span>
    </>
};

Please not the double arrow function const _inc = () => c => c+1;. If needed, first function argument is the SyntheticEvent returned by React. Keep in mind that SyntheticEvent are immediately destroyed by React after callback. So because these functions are memoized, the SyntheticEvent event will be lost after first call. To bypass this, we trigger a SyntheticEvent.persist() before memoization. Second function argument is the current state value.

const _setValue = ({target:{value}}) => () => value;
const MyInput = () => {
    const [ value,,, { setValue } ] = useState("", {
		setValue: _setValue,
	});

    return <>
        <input onChange={setValue} value={value} />
    </>
};