javascript - 如何在 TypeScript 中将数组转换为对象？

Question

我正在尝试输入下面的实用函数，它接受一个数组并返回一个对象，如下所示

const convertListToMap = (list, key, secondKey) => {
  const map = {};
  
  for (const ele of list) {
    map[ele[key]] = ele[secondKey]
  }
  
  return map;
}


console.log(convertListToMap([{name: 'isaac', age: 17}, {name: 'john', age: 20}], 'name', 'age'));

console.log(convertListToMap([{race: 'chinese', language: 'mandarin'}, {race: 'malay', language: 'melayu'}], 'race', 'language'));

如你所知key和 secondKey是动态的，取决于参数 list ，所以我猜 generics是要走的路。下面是我的尝试

const convertListToMap = <
  T extends object,
  U extends keyof T,
  V extends keyof T
>(
  list: T[],
  key: U,
  secondKey: V
) => {
  const map = {} as Record<U, V>;
  for (const ele of list) {
    map[ele[key]] = ele[secondKey];
  }
  return map;
};

但是，上面给出了错误 Type 'T[U]' cannot be used to index type 'Record<U, V>' , 想知道我做错了哪一部分？

更新

我最近的尝试是更新 map 的签名如下

  const map = {} as Record<T[U], T[V]>;
  for (const ele of list) {
    map[ele[key]] = ele[secondKey];
  }
  return map;

通过这次最新尝试，将值分配给 map变量很好，但我在 Record 声明行遇到错误，错误如下

Type 'T[U]' does not satisfy the constraint 'string | number | symbol'.Type 'T[keyof T]' is not assignable to type 'string | number | symbol'.Type 'T[string] | T[number] | T[symbol]' is not assignable to type 'string | number | symbol'.Type 'T[string]' is not assignable to type 'string | number | symbol'.Type 'T[string]' is not assignable to type 'symbol'.Type 'T[keyof T]' is not assignable to type 'symbol'.Type 'T[U]' is not assignable to type 'symbol'.Type 'T[keyof T]' is not assignable to type 'symbol'.Type 'T[string] | T[number] | T[symbol]' is not assignable to type 'symbol'.Type 'T[string]' is not assignable to type 'symbol'.ts(2344)

Answer 1

最后一次尝试的问题是 Record似乎只期待string | number | symbol ，并且由于 TypeScript 不确定是什么 T[U]会的，因此它引发了错误。我发现我们可以告诉 TS 更多关于 T 的信息如下

const convertListToMap = <
  T extends { [key: string|number]: string | number },
  U extends keyof T,
  V extends keyof T
>(
  list: T[],
  key: U,
  secondKey: V
) => {
  const map = {} as Record<T[U], T[V]>;
  for (const ele of list) {
    map[ele[key]] = ele[secondKey];
  }
  return map;
};

从上面，我们告诉 typescript T将成为 key 的对象的 string , 并且该值将是 string | number 类型，因此，TypeScript 对定义 Record<T[U], T[V]> 很满意

这个解决方案效果很好，TS 可以正确推断

const personObj = convertListToMap([{name: 'isaac', age: 17}, {name: 'john', age: 20}], 'name', 'age')
// const personObj: Record<string, number>

const languageObj = convertListToMap([{race: 'chinese', language: 'mandarin'}, {race: 'malay', language: 'melayu'}], 'race', 'language')
// const languageObj: Record<string,string>