<!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>