利用typescript类型系统改进我的代码

Question

我很好奇TypeScript是否能在这个问题上帮我。

我的项目有文本消息、媒体消息、键盘消息和事件消息。

interface Message {
  kind: 'text' // can be `text`, `media`, `keyboard` or `event` 
}

每种类型都有自己的属性，比如image就有预览。

目前我们所拥有的是这样的东西

export type MessageKind = 'text' | 'media' | 'keyboard' | 'event'

export interface MessageSchema {
  id: string // common to all messages
  kind: MessageKind // common to all messages
  room: string // common to all messages

  // now come the specific fields and sadly all optionals.
  filename?: string // specific of the "kind" media
  caption?: string // specific of the "kind" media
  mimetype?: string // specific of the "kind" media
  orientation?: 'portrait' | 'landscape'  // specific of the "kind" media

  rows?: number // specific of the "kind" keyboard
  columns?: number // specific of the "kind" keyboard

  price?: number // specific of the "kind" event
  balance?: number // specific of the "kind" event
  charged?: boolean // specific of the "kind" event
}

如何才能在不滥用可空类型的情况下设计出更好的解决方案？

Answer 1

您可以对公共字段使用交叉点类型，然后对所有种类特定的字段使用联合：

export type MessageSchema = {
    id: string;
    room: string;
} & (
    | {
          kind: "text";
      }
    | {
          kind: "media";
          filename: string;
          caption: string;
          mimetype: string;
          orientation: "portrait" | "landscape";
      }
    | {
          kind: "keyboard";
          rows: number;
          columns: number;
      }
    | {
          kind: "event";
          price: number;
          balance: number;
          charged: boolean;
      }
);