关于javascript proto3

Question

syntax = "proto3";
package tutorial;

message AddressBook {
  repeated Person people = 1;
}

message Person {
  string num = 1;
  **MyMessage dypluser = 2;**//为什么在js这里会提示undefined 而在python 可以正常使用？
}

message MyMessage {
    repeated listas lista = 1;
  }

  message listas {
    int32 gender = 1;
  }