What is the question mark for in a Typescript parameter name

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;
  }
}

In id? what's the ? for?

It is to mark the parameter as optional.

• TypeScript handbook https://www.typescriptlang.org/docs/handbook/2/functions.html#optional-parameters

• TypeScript Deep Dive https://basarat.gitbook.io/typescript/type-system/functions#optional-parameters

Stack Overflow Q#37632760, score: 353