异步map+filter转单遍异步reduce报错，如何正确改写？

原可运行代码 #

const incompleteKYCClaims = await Promise.all(
  kycPendingProviders.map(async (p) => {
    const provider = await getProviderOrThrow(p.tin)

    const isPreviouslyApproved = provider.stripeAccount != undefined    
    if (isPreviouslyApproved) {
      return
    }
  
    return toProviderRelationshipClaims({ tin: p.tin, role: ProviderUserSubRoles.ky, status: 'KYCInDraft' })
  })
)
const incompleteKYCClaimsFiltered = incompleteKYCClaims.filter(
  (claim) => claim
) as Array<ProviderRelationshipClaims>

尝试的reduce版本（存在错误） #

const incompleteKYCClaims = kycPendingProviders.reduce<Array<ProviderRelationshipClaims>>( async (filtered, p) => {
  const provider = await getProviderOrThrow(p.tin)

  const isPreviouslyApproved = previouslyApproved.includes(provider.status)

  if (!isPreviouslyApproved) {
    filtered.push(toProviderRelationshipClaims({tin: p.tin, role: ProviderUserSubRoles.ky, status: 'KYCInDraft'}))
  }
  return filtered
}, Promise.resolve([]) as Array<ProviderRelationshipClaims>

报错信息 #

Argument of type '(filtered: ProviderRelationshipClaims[], p: ProviderRelationship) => Promise<ProviderRelationshipClaims[]>' is not assignable to parameter of type '(previousValue: ProviderRelationshipClaims[], currentValue: ProviderRelationship, currentIndex: number, array: ProviderRelationship[]) => ProviderRelationshipClaims[]'.

修复方案 #

错误根源在于：reduce回调是async函数，返回值为Promise<Array<ProviderRelationshipClaims>>，但你给reduce指定的泛型是Array<ProviderRelationshipClaims>，且初始值的类型断言错误。另外，每一轮reduce的累积值是Promise，必须先await解析才能操作数组。

修复后的代码如下：

const incompleteKYCClaims = await kycPendingProviders.reduce<Promise<Array<ProviderRelationshipClaims>>>(
  async (filteredPromise, p) => {
    // 先解析上一轮的累积Promise，得到当前可操作的数组
    const filtered = await filteredPromise;
    const provider = await getProviderOrThrow(p.tin);

    // 注意：此处还原原代码的判断逻辑，若你确实需要改用previouslyApproved.includes请自行调整
    const isPreviouslyApproved = provider.stripeAccount != undefined;
    if (!isPreviouslyApproved) {
      filtered.push(toProviderRelationshipClaims({
        tin: p.tin,
        role: ProviderUserSubRoles.ky,
        status: 'KYCInDraft'
      }));
    }
    return filtered;
  },
  Promise.resolve([]) // 初始值为已resolve的空数组Promise
);

关键修复点： #

1. 泛型修正：将reduce的泛型指定为Promise<Array<ProviderRelationshipClaims>>，匹配回调的返回值类型
2. 解析累积Promise：在回调开头await filteredPromise，获取当前可操作的数组
3. 初始值修正：直接使用Promise.resolve([])，无需错误的类型断言
4. 逻辑对齐：还原原代码中isPreviouslyApproved的判断逻辑，避免因逻辑变更引入新问题

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