如何将表单转换成json通过AJAX传递？

var a = JSON.parse("{\"question\":[],\"user\":[]}");
            var QstObj = {
                questionId:"",
                currectAnswer:""
            }
            var UserObj = {
                userType:""
            }
             
            var q_Sum = $("li").length;
            for(var i = 0; i < q_Sum;i++){
            var j = i+1;
            var QstObj = new  Object();
            var UserObj = new Object();
            QstObj.questionId = $("#questionId"+i).val();
            QstObj.currectAnswer = $(".q"+j).find(".checked > input").val();
            a.question.push(QstObj);
            }
            UserObj = GetToken();
            UserObj.userType = "0";
            a.user.push(UserObj);
                    var obj=JSON.stringify(a);
             
            }