索引签名类型

Question

我在试图为以下内容编写类型时遇到了困难：

type Language = 'en' | 'nl';

interface CacheObject {
  [key: string | number | Language]: string;
}

const cache: CacheObject = {};

export const init = (dir: string): Promise<void> =>
  fsPromises.readdir(dir).then(files =>
    files
      .filter(files => files.endsWith('.json'))
      .forEach(async file => {
        cache[file.slice(0, -5)] = await import(`${dir}/${file}`);
      })
  );

export const translate = (lang: Language): any => (key: string) =>
  key.split('.').reduce((acc, val) => acc[val], cache[lang]);

问题如下：

const cache: CacheObject
Element implicitly has an 'any' type because expression of type 'string' can't be used to index type 'CacheObject'.
  No index signature with a parameter of type 'string' was found on type 'CacheObject'.

const cache: CacheObject
Element implicitly has an 'any' type because expression of type 'Language' can't be used to index type 'CacheObject'.
  Property 'en' does not exist on type 'CacheObject'.

有人能帮我指出正确的方向吗？

Answer 1

您忽略了正在得到的另一个错误：An index signature parameter type must be 'string' or 'number' ( TS中可能有另一个错误，该错误可能会被其他错误所抑制)，在测试代码时，错误会丢失，但在对代码进行一些非相应的更改后出现。玩弄错误)

如果要使用Languages向类型添加一些已知元素，则需要在交集中使用包含索引签名的类型的映射类型：

type CacheObject = {
  [key: string]: string;
  [key: number]: string;
} & Partial<Record<Language, string>>

玩

如果您只有索引签名来保持编译器对字符串索引的沉默，但是对象只能包含您可以考虑转换索引表达式的语言：

type CacheObject = Partial<Record<Language, string>>
cache[file.slice(0, -5) as Language] = await import(`${dir}/${file}`);

玩