html
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>js引入方式</title>
<!-- <script>
alert("hello js");
</script> -->
<script src="js/demo.js"></script>
</head>
<body>
</body>
</html>