<!DOCTYPE html>
<html>
<head>
<meta name="viewport" content="width=device-width, minimum-scale=1.0">
<title>Page with focus event handler</title>
</head>
<body>
<input id="input" type="text">
<script>
let focus_fired = false;
document.getElementById('input').addEventListener('focus', () => {
focus_fired = true;
});
</script>
</body>
</html>