如何修复TypeScript错误：元素隐式'any'类型无法索引空对象

错误原因 #

代码中reduce的初始值为{}，TypeScript默认将其推断为{}类型。当使用字符串类型的modifiedKey为该对象赋值时，由于空对象未定义字符串索引签名，触发类型错误。

修复方案 #

方案1：给初始值添加类型断言

通过as Record<string, string>明确初始值是键值均为字符串的对象：

const a = {
  '/app/developer-tools/API-keys': '/app/developer-tools/API-keys',
  '/app/developer-tools/API-reference': '/app/developer-tools/API-reference',
  '/app/engage': '/app/engage',
};

export const modifiedPaths = Object.keys(a).reduce((acc, key) => {
  const modifiedKey = key.replace("/app/", "");
  acc[modifiedKey] = a[key];
  return acc;
}, {} as Record<string, string>);

方案2：为reduce指定泛型参数

提前定义返回对象的类型，通过泛型参数告知TypeScript累加器的类型：

const a = {
  '/app/developer-tools/API-keys': '/app/developer-tools/API-keys',
  '/app/developer-tools/API-reference': '/app/developer-tools/API-reference',
  '/app/engage': '/app/engage',
};

type ModifiedPaths = {
  [key: string]: string;
};

export const modifiedPaths = Object.keys(a).reduce<ModifiedPaths>((acc, key) => {
  const modifiedKey = key.replace("/app/", "");
  acc[modifiedKey] = a[key];
  return acc;
}, {});

方案3：精确类型推导（保留修改后键的字面量类型）

如果需要让modifiedPaths的键为原键去掉/app/后的具体字面量类型，可使用以下写法：

const a = {
  '/app/developer-tools/API-keys': '/app/developer-tools/API-keys',
  '/app/developer-tools/API-reference': '/app/developer-tools/API-reference',
  '/app/engage': '/app/engage',
} as const;

type OriginalKeys = keyof typeof a;
type ModifiedKeys = OriginalKeys extends `/app/${infer Rest}` ? Rest : never;

export const modifiedPaths = Object.keys(a).reduce((acc, key) => {
  const modifiedKey = key.replace("/app/", "") as ModifiedKeys;
  acc[modifiedKey] = a[key];
  return acc;
}, {} as Record<ModifiedKeys, string>);

此方案下modifiedPaths的键会被精确推断为'developer-tools/API-keys'、'developer-tools/API-reference'、'engage'，而非宽泛的string类型。

内容的提问来源于stack exchange，提问作者merlin