вы можете сохранять и читать данные вот так
const nameTxt = document.querySelector('#name');
const date = document.querySelector('#date');
nameTxt.addEventListener('change', (event) => {
localStorage.setItem('name', event.target.value);
});
date.addEventListener('change', (event) => {
localStorage.setItem('date', event.target.value);
});
function getSavedData() {
console.log('name', localStorage.getItem('name'));
console.log('date', localStorage.getItem('date'));
}
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Document</title>
</head>
<body>
<label for="eventlocation">Event Location (1 to 20 characters):</label>
<input type="text" id="name" name="name" required minlength="1" maxlength="20"
size="20">
<label for="datetime">Event Date and Time:</label>
<input type="datetime-local" id="date" name="date" required minlength="1"
maxlength="20" size="20">
<script src="app.js"></script>
</body>
</html>