TypeScript报错TS(7015)：索引表达式非number类型致隐式any

这个错误的根源是Object.keys()返回的是string[]类型，而数组communes的合法索引必须是number类型。TypeScript无法确认遍历到的key是有效的数字索引，因此将communes[key]推断为any类型，触发了类型错误。

下面是几种可行的解决方法：

方案一：直接遍历数组元素（推荐） #

数组遍历优先使用forEach直接迭代元素，完全规避索引类型不匹配的问题，代码更简洁：

const communes: ICommune[] = _.filter(wilayasData, (commune) => commune.wilaya_code === wilaya.wilaya_code);
communes.forEach((commune) => {
  commune.commune = commune.commune_name_ascii;
  commune.commune_ar = commune.commune_name;
  commune.daira = commune.daira_name_ascii;
  commune.daira_ar = commune.daira_name;
  delete commune.commune_name_ascii;
  delete commune.commune_name;
  delete commune.daira_name_ascii;
  delete commune.daira_name;
});

方案二：将key转换为数字类型 #

如果必须保留Object.keys的使用，可以把字符串类型的key转为数字，再进行类型断言：

const communes: ICommune[] = _.filter(wilayasData, (commune) => commune.wilaya_code === wilaya.wilaya_code);
Object.keys(communes).forEach((key) => {
  const index = parseInt(key, 10);
  const commune = communes[index] as ICommune;
  commune.commune = commune.commune_name_ascii;
  commune.commune_ar = commune.commune_name;
  commune.daira = commune.daira_name_ascii;
  commune.daira_ar = commune.daira_name;
  delete commune.commune_name_ascii;
  delete commune.commune_name;
  delete commune.daira_name_ascii;
  delete commune.daira_name;
});

方案三：类型断言确认key为合法索引 #

通过类型断言告诉TypeScript，Object.keys返回的是数组的合法数字索引：

const communes: ICommune[] = _.filter(wilayasData, (commune) => commune.wilaya_code === wilaya.wilaya_code);
(Object.keys(communes) as Array<keyof typeof communes>).forEach((key) => {
  communes[key].commune = communes[key].commune_name_ascii;
  communes[key].commune_ar = communes[key].commune_name;
  communes[key].daira = communes[key].daira_name_ascii;
  communes[key].daira_ar = communes[key].daira_name;
  delete communes[key].commune_name_ascii;
  delete communes[key].commune_name;
  delete communes[key].daira_name_ascii;
  delete communes[key].daira_name;
});

优先推荐方案一，既符合数组遍历的最佳实践，又彻底解决了类型问题，代码可读性最高。

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