$(f).validate is not a function点击快时出错..急!

function init(){
//表单验证
var f=document.forms['f'];
$(f).validate({//点击快时出错
submitHandler:function(form){
if($('.bluebtn').html()=='正在提交.') return;
$('.bluebtn').html('正在提交.');
$.ajax({
url:'/business/save',
type:'post',
data:$(form).formSerialize(),
success:function(msg){
if(msg=='ok'){
alert("保存成功。");
goUrl('business/index');
}else{
alert(msg);
//alert("你输入符号里存在字符冲突!");
$('.bluebtn').html('确　定');
}
}
});
}
});