js 判断字符串, 对象是否为空
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<script type="text/javascript" src="Scripts/jquery/jquery-1.7.2.min.js"></script>
<title></title>
</head>
<body>
<input id="username" type="text" placeholder="输入用户名" />
<input type="button" value="测试" onclick="test()"/>
<script type="text/javascript">
function test() {
var username = $("#username").val();
// 方法一
if(username){
alert("对象不为空！");
}
// 或者
if (typeof username == "undefined" || username == null || username == '') {
alert("空对象");
} else {
alert("对象不为空！");
}
}
</script>
</body>
</html>
