JavaScriptの基本

<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Script</title>
</head>
<body>
<script>
alert("Hello world!!");
</script>
</body>
</html>

 <!DOCTYPE html>
<head>
<meta charset="UTF-8">
<title>Script</title>
</head>
<body>
本文
<script src="script.js"></script>
</body>
</html>