Ciro Santilli
OurBigBook.com
web-cheat/react/prop-change-hook-use-memo.html
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8" />
<script src="https://unpkg.com/react@17/umd/react.development.js"></script>
<script src="https://unpkg.com/react-dom@17/umd/react-dom.development.js"></script>
<script src="https://unpkg.com/@babel/standalone@7.14.7/babel.min.js"></script>
</head>
<body>
<p><a href="https://cirosantilli.com/react">https://cirosantilli.com/react</a></p>
<div id="root"></div>
<script type="text/babel">
function NotMain2(props) {
console.log('NotMain2');
const [n, setN] = React.useState(props.n)
return (
<>
<div>NotMain2 props.n = {props.n}</div>
<div>NotMain2 n = {n}</div>
</>
)
}
function React.useMemo(NotMain(props) {
console.log('NotMain');
const [n, setN] = React.useState(props.n)
return (
<>
<div>NotMain props.n = {props.n} n = {props.n}</div>
<NotMain2 n={props.n} />
</>
)
})
function Main(props) {
console.log('Main');
const [n, setN] = React.useState(0)
function handleClick() {
console.log('handleClick\n');
setN(n + 1)
}
return (
<div>
<div onClick={handleClick}>Click me twice</div>
<div>Main n = {n}</div>
<NotMain n={Math.floor(n / 2)}></NotMain>
</div>
)
}
ReactDOM.render(
<Main/>,
document.getElementById('root')
);
</script>
</body>
</html>