TypeScript数组reduce累加器类型定义报错问题求助

问题原因 #

报错的核心在于reduce方法的初始值{}被TypeScript默认推断为空对象类型{}，即便你给累加器参数acc标注了Partial<IWithdrawalRequest>，初始值的类型与参数类型不匹配，导致TypeScript认为acc[key]只能是undefined，无法兼容payoutFields[key]的string | number类型。

解决方案 #

方案1：给初始值显式指定类型 #

直接通过类型断言给初始值{}指定Partial<IWithdrawalRequest>类型，让初始值与累加器参数的类型保持一致：

private buildRequestBody(payoutFields: IWithdrawalRequest): ISignedWithdrawalRequest {
  const sortedPayoutFieldKeys = Object.keys(payoutFields)
    .sort() as Array<keyof IWithdrawalRequest>;

  const requestBody = sortedPayoutFieldKeys.reduce((acc: Partial<IWithdrawalRequest>, key) => {
    acc[key] = payoutFields[key];
    return acc;
  }, {} as Partial<IWithdrawalRequest>); // 显式指定初始值类型

  ...
}

方案2：使用reduce的泛型参数明确累加器类型 #

通过reduce<Partial<IWithdrawalRequest>>的泛型声明，直接告诉TypeScript累加器的类型，无需单独给acc参数标注类型：

private buildRequestBody(payoutFields: IWithdrawalRequest): ISignedWithdrawalRequest {
  const sortedPayoutFieldKeys = Object.keys(payoutFields)
    .sort() as Array<keyof IWithdrawalRequest>;

  const requestBody = sortedPayoutFieldKeys.reduce<Partial<IWithdrawalRequest>>((acc, key) => {
    acc[key] = payoutFields[key];
    return acc;
  }, {});

  ...
}

补充说明 #

• Partial<IWithdrawalRequest>会将IWithdrawalRequest的所有属性转为可选类型，完美匹配初始空对象的状态，同时允许逐步赋值。
• 如果后续需要将requestBody转为完整的IWithdrawalRequest，可以在后续逻辑中使用类型断言（如requestBody as IWithdrawalRequest），前提是你能确保所有必要属性都已被赋值。

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