ajax 的三种使用方法

        <form method="post" action="./index.php">
            <input name="username" placeholder="用户名"  type="text"  >
            <input name="password"placeholder="密码" type="password">
            <input value="登录" type="submit">
        </form>

$.post(路径,{"data":data},function(a){
    alert(a);
},"json");

$.ajax({
   url:"./index.php",
   type:"post",
   data:{username:username},
   jsonType:"json",
   success:function(a){
      alert(a)
   },
   error:function(e){
      alert("错误");
    }
});