一个？语法问题

[zhongjixiuxing]

看到下面的代码, `我不明白代码中的？用法, 加不加问号有什么区别吗？

export class Thread {
  id: string;
  lastMessage: Message;
  name: string;
  avatarSrc: string;

  constructor(id?: string,
              name?: string,
              avatarSrc?: string) {
    this.id = id || uuid();
    this.name = name;
    this.avatarSrc = avatarSrc;
  }
}

[hstarorg]

可选参数。

[ShiYuanjun-Tim]

this is the typescript syntax , means this is an optional parameter