<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title></title>
<script src="js/jquery-1.8.3.js"></script>
</head>
<body>
<input type="text" id="username" value="jack" />
</body>
<script type="text/javascript">
//通过dom获取
var username=document.getElementById("username");
//弹出值
//alert(username.value);
//通过$(选择器)获取jquery对象
var $username=$("#username");
//通过jquery对象的val()方法获取value属性
alert($username.val());
</script>
</html>
