先给大家看下这个效果：
未输入值
输入值后
输入值后以下是源代码：
<!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=gb2312" />
<title>登录提示框</title>
<script src="http://ajax.googleapis.com/ajax/libs/jquery/1.7.2/jquery.min.js" type="text/javascript"></script>
<script type="text/javascript">
$(document).ready(function () {
$("#TxtUserName").focus(function () {
$(this).attr({ style: "border-color:#FFA91A;" });
if ($(this).val() == "用户名")
$(this).attr("value", "");
$(this).attr({ style: "color:#653C31;" });
});
$("#TxtUserName").blur(function () {
$(this).attr({ style: "border-color:#c1c1c1;" });
if ($(this).val() == "") {
$(this).attr("value", "用户名");
} else {
$(this).attr({ style: "color:#653C31;" });
}
});
$("#TxtPassword").blur(function () {
if ($(this).val() == "") {
$(this).attr({ style: "display:none" });
$("#userpwd_a").attr({ style: "display:" });
$("#userpwd_a").attr("value", "密码");
}
else {
$(this).attr({ style: "border-color:#c1c1c1;color:#653C31;" });
}
});
$("#userpwd_a").focus(function () {
if ($("#TxtPassword").val() == "") {
$(this).attr({ style: "display:none" });
$("#TxtPassword").attr({ style: "border-color:#FFA91A;display:" });
$("#TxtPassword").val("");
$("#TxtPassword").focus();
} else {
$(this).attr({ style: "display:none" });
$("#TxtPassword").attr({ style: "border-color:#FFA91A;display:" });
$("#TxtPassword").focus();
}
});
$("#TxtPassword").focus(function () {
$(this).attr({ style: "border-color:#FFA91A;color:#653C31;" });
$(this).attr("value", "");
});
});
</script>
<style type="text/css">
input{ color:red;}
</style>
</head>
<body>
<div class="outbox">
<ul class="login">
<li style="position:relative;">
<input class="username" type="text" value="用户名" maxlength="24" id="TxtUserName"/>
</li>
<li>
<input type="text" id="userpwd_a" class="userpwd" value="密码" maxlength="24" />
<input class="userpwd" type="password" value="" maxlength="24" id="TxtPassword" style="display:none"/>
</li>
</ul>
</div>
</body>
</html>
生成验证码在下篇文章中讲解： 生成验证码及判断是否匹配