index.html
<!DOCTYPE html>
<html lang="ja">
<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>My JavaScript</title>
</head>
<body>
<input type="text">
<p></p>
<script src="main.js"></script>
</body>
</html>main.js
'use strict';
{
// input → text, textarea, select
// change → radio, checkbox
document.querySelector('input').addEventListener('input', () => {
const pElement = document.querySelector('p');
const inputElement = document.querySelector('input');
// pElement.textContent = inputElement.value;
pElement.textContent = inputElement.value.length;
});
}