如何创建既强制含所有键又能推断值类型的TypeScript映射？

假设我们有如下键类型：

type State = "OPEN" | "CLOSED";

方案一：使用无类型object #

const stateToNaturalLangMap = {
  OPEN: "open",
  CLOSED: "closed"
} as const;

// "OPEN" | "CLOSED"
type KeysOfMap = keyof typeof stateToNaturalLangMap;

// "open" | "closed"
type ValuesOfMap = (typeof stateToNaturalLangMap)[keyof typeof stateToNaturalLangMap];

该方案能自动推断键和值的具体类型，但无法强制映射包含所有指定的State键，也不能限制额外键的添加。

方案二：使用Record #

const stateToNaturalLangRecord: Record<State, string> = {
  OPEN: "open",
  CLOSED: "closed"
} as const;

// "OPEN" | "CLOSED"
type KeysOfRecord = keyof typeof stateToNaturalLangRecord;

// string
type ValuesOfRecord = (typeof stateToNaturalLangRecord)[keyof typeof stateToNaturalLangRecord];

该方案刚好相反：它强制映射包含所有State键，且不允许添加额外键，但无法推断值的具体类型，值类型只能被识别为宽泛的string。

正确解决方案 #

方法1：泛型函数约束（兼容全版本TypeScript） #

通过泛型函数实现类型约束与类型推断的兼顾：

type State = "OPEN" | "CLOSED";

function createStateMap<T extends Record<State, string>>(map: T): T {
  return map;
}

const stateToNaturalLang = createStateMap({
  OPEN: "open",
  CLOSED: "closed"
} as const);

// "OPEN" | "CLOSED"
type KeysOfMap = keyof typeof stateToNaturalLang;

// "open" | "closed"
type ValuesOfMap = (typeof stateToNaturalLang)[keyof typeof stateToNaturalLang];

这里用T extends Record<State, string>约束传入对象必须包含所有State键，同时返回类型为T以保留值的具体类型。若遗漏State键或添加额外键，TypeScript会直接报错；值的类型也会被精确推断为字面量类型。

方法2：satisfies运算符（TypeScript 4.9+） #

利用satisfies运算符可以更简洁地实现需求：

type State = "OPEN" | "CLOSED";

const stateToNaturalLang = {
  OPEN: "open",
  CLOSED: "closed"
} as const satisfies Record<State, string>;

// "OPEN" | "CLOSED"
type KeysOfMap = keyof typeof stateToNaturalLang;

// "open" | "closed"
type ValuesOfMap = (typeof stateToNaturalLang)[keyof typeof stateToNaturalLang];

satisfies会检查对象是否符合指定类型，但不会覆盖对象的原始类型推断，完美实现了“强制包含指定键+自动推断值类型”的双重需求。

内容的提问来源于stack exchange，提问作者Hans