如何在TypeScript中实现支持多层级嵌套的RequireOnlyOne类型

实现方案 #

我们可以直接嵌套复用已有的RequireOnlyOne类型，先后对二级属性、一级属性做单属性互斥约束即可满足需求。

1. 复用基础的RequireOnlyOne类型

type RequireOnlyOne<T, Keys extends keyof T = keyof T> =
  Pick<T, Exclude<keyof T, Keys>>
  & {
      [K in Keys]-?:
          Required<Pick<T, K>>
          & Partial<Record<Exclude<Keys, K>, undefined>>
  }[Keys]

2. 原有MenuItems接口定义

export interface MenuItems {
  firstLevel: {
    secondLevel: ['one', 'two']
  };
  anotherFirstLevel: {
    anotherSecondLevel: ['one', 'two'],
    oneMoreSecondLevel: null
  };
}

3. 组合生成目标类型customType

// 第一步：先约束每个一级属性对应的二级对象只能存在1个二级属性
type SecondLevelConstrained = {
  [K in keyof MenuItems]: RequireOnlyOne<MenuItems[K]>
}

// 第二步：约束顶层对象只能存在1个一级属性
type customType = RequireOnlyOne<SecondLevelConstrained>

4. 效果验证

// 正常通过类型校验
const workingObject: customType = {
  firstLevel: {
    secondLevel: ['one', 'two']
  }
}

// 触发报错：同时存在2个一级属性
const errorObject: customType = {
  firstLevel: {
    secondLevel: ['one', 'two']
  },
  anotherFirstLevel: {
    anotherSecondLevel: ['one', 'two']
  }
}

// 触发报错：一级属性下同时存在2个二级属性
const anotherErrorObject: customType = {
  anotherFirstLevel: {
    anotherSecondLevel: ['one', 'two'],
    oneMoreSecondLevel: null
  }
}

内容的提问来源于stack exchange，提问作者Cristian Blandon