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14-lazy-initialization.html
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<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8" />
<meta http-equiv="X-UA-Compatible" content="IE=edge" />
<meta name="viewport" content="width=device-width, initial-scale=1.0" />
<title>14-lazy-initialization</title>
</head>
<body>
<div id="root"></div>
<!-- URL's changed for react libs. `React.useState not defined in [email protected]` -->
<script src="https://unpkg.com/[email protected]/umd/react.development.js"></script>
<script src="https://unpkg.com/[email protected]/umd/react-dom.development.js"></script>
<script src="https://unpkg.com/@babel/[email protected]/babel.js"></script>
<script type="text/babel">
const rootEl = document.getElementById("root");
const Greeting = () => {
const [name, setName] = React.useState(() => {
console.log("hello");
return window.localStorage.getItem("form-name") || "";
});
console.log("rendered");
React.useEffect(() => {
window.localStorage.setItem("form-name", name);
});
const handleChange = (event) => setName(event.target.value);
return (
<div>
<form>
<label htmlFor="frm-name">Name: </label>
<input value={name} onChange={handleChange} id="frm-name" />
</form>
<p>
{name ? <strong>Hello {name}</strong> : "Please type your name"}
</p>
</div>
);
};
ReactDOM.render(<Greeting />, rootEl);
</script>
</body>
</html>