required：“#aa：checked” //表达式值为真时需要验证
required：function(){} //返回为真时需要验证
示例
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>表单验证需同时填或不填的元素</title>
<script src="https://static.runoob.com/assets/jquery-validation-1.14.0/lib/jquery.js"></script>
<script src="https://static.runoob.com/assets/jquery-validation-1.14.0/dist/jquery.validate.min.js"></script>
<script src="https://static.runoob.com/assets/jquery-validation-1.14.0/dist/localization/messages_zh.js"></script>
<script>
$.validator.setDefaults({
submitHandler: function() {
alert("提交事件!");
}
});
$().ready(function() {
// 点击“我乐意接收新信息”的复选框时启动该方法
// 选择框默认不可见，选中复选框时移除hidden属性，取消复选框时加入hidden属性
$("#newsletter").click(function(){
// 获取主题选择框的hidden属性
var hideAttr = $("#newsletter_topics").attr("hidden");
if(hideAttr === "hidden"){
// 若hidden属性存在且值为hidden时，将这个属性移除，选择框就可见了
$("#newsletter_topics").removeAttr("hidden");
} else {
// 上一次点击时移除了hidden属性，再次点击时加上hidden属性并将其值设为“hidden”，选择框就不可见了
$("#newsletter_topics").attr("hidden", "hidden");
}
})
// 在键盘按下并释放及提交后验证提交表单
$("#signupForm").validate({
rules: {
firstname: "required",
lastname: "required",
username: {
required: true,
minlength: 2
},
password: {
required: true,
minlength: 5
},
confirm_password: {
required: true,
minlength: 5,
equalTo: "#password"
},
email: {
required: true,
email: true
},
"topic[]": {
required: "#newsletter:checked",
minlength: 2
},
agree: "required"
},
messages: {
firstname: "请输入您的名字",
lastname: "请输入您的姓氏",
username: {
required: "请输入用户名",
minlength: "用户名必需由两个字母组成"
},
password: {
required: "请输入密码",
minlength: "密码长度不能小于 5 个字母"
},
confirm_password: {
required: "请输入密码",
minlength: "密码长度不能小于 5 个字母",
equalTo: "两次密码输入不一致"
},
email: "请输入一个正确的邮箱",
agree: "请接受我们的声明",
topic: "请选择两个主题"
}
});
});
</script>
<style>
.error{
color:red;
}
</style>
</head>
<body>
<form class="cmxform" id="signupForm" method="get" action="">
<fieldset>
<legend>验证完整的表单</legend>
<p>
<label for="firstname">名字</label>
<input id="firstname" name="firstname" type="text">
</p>
<p>
<label for="lastname">姓氏</label>
<input id="lastname" name="lastname" type="text">
</p>
<p>
<label for="username">用户名</label>
<input id="username" name="username" type="text">
</p>
<p>
<label for="password">密码</label>
<input id="password" name="password" type="password">
</p>
<p>
<label for="confirm_password">验证密码</label>
<input id="confirm_password" name="confirm_password" type="password">
</p>
<p>
<label for="email">Email</label>
<input id="email" name="email" type="email">
</p>
<p>
<label for="agree">请同意我们的声明</label>
<input type="checkbox" class="checkbox" id="agree" name="agree">
</p>
<p>
<label for="newsletter">我乐意接收新信息</label>
<input type="checkbox" class="checkbox" id="newsletter" name="newsletter">
</p>
<!--属性hidden隐藏主题选择框，给“我乐意接收新信息”的复选框绑定点击事件，来控制主题选择框的可见性-->
<fieldset hidden="hidden" id="newsletter_topics">
<legend>主题 (至少选择两个) - 注意：如果没有勾选“我乐意接收新信息”以下选项会隐藏，但我们这里作为演示让它可见</legend>
<label for="topic_marketflash">
<input type="checkbox" id="topic_marketflash" value="marketflash" name="topic[]">Marketflash
</label>
<label for="topic_fuzz">
<input type="checkbox" id="topic_fuzz" value="fuzz" name="topic[]">Latest fuzz
</label>
<label for="topic_digester">
<input type="checkbox" id="topic_digester" value="digester" name="topic[]">Mailing list digester
</label>
<label for="topic" class="error" style="display:none">至少选择两个</label>
</fieldset>
<p>
<input class="submit" type="submit" value="提交">
</p>
</fieldset>
</form>
</body>
</html>
