<!DOCTYPE HTML>
<html lang="en-US">
<head>
<meta charset="UTF-8">
<title>2.13.JavaScript.条件语句</title>
</head>
<body>
<script type="text/javascript">
/*
//if else语句
if( 100 > 10 ){
document.write("真");
}else{
document.write("假");
}
*/
//
function checkChange(){
var username = document.getElementById("username");//获取到html节点
if( username.value == ""){
alert("用户名不能为空");
}else if( username.value == "admin" || username.value == "xiaozhanga4"){
alert("恭喜你，" + username.value);
}else{
alert("用户名错误");
}
}
</script>
<form method="post" action="">
<input type="text" name="username" id="username"/>
<input type="submit" value="提交" onclick="checkChange();"/>
</form>
</body>
</html>