ajax中contentType为application/json的用法

不使用contentType: "application/json"，则data可以是对象

$.ajax({
  url: url,
  type: "post",
  datType: "json",
  data: { id: user_id },
  async: false,
  success: function () {}
});

使用contentType: "application/json"，则data只能是json字符串

$.ajax({
  url: url,
  type: "post",
  datType: "json",
  contentType: "application/json"
  data: "{'id': " + user_id +"}",
  async: false,
  success: function () {}
});