<!DOCTYPE html>
<html lang="zh">
<head>
<meta charset="UTF-8" />
<meta name="viewport" content="width=device-width, initial-scale=1.0" />
<meta http-equiv="X-UA-Compatible" content="ie=edge" />
<title>jQuery库</title>
<script src="js/jquery-3.2.1.js"></script><!--引入jQuery库-->
<script>
$(document).ready(function(){
alert("hello world！！");
});
</script>
</head>
<body>
</body>
</html>
$(document).ready(function{ }) 和 window.onload=function() 等价
