Object.defineProperty2-解决方案

function getObj() {
        let obj = {
            sex:"男",
            age:18
        };
        let val = ""; //此处val是安全的,外部是无法修改的
        let o = Object.defineProperty(obj, "key", {
          configurable: true,
          enumerable: true,
          get: function () {
            return val || 0;
          },
          set: function (n) {
            val = n;
          },
        });
        return o; //每个对象都是新的
      }
      let aa = getObj();
      console.log(aa.sex); //返回性别