Question

我希望Typescript推断过滤数组上的类型。

我正在根据状态“已拒绝”或“已满”（来自Promise.allSettled）过滤结果。

由于某种原因，Typescript无法推断我的过滤结果。
这是我要实现的目标的最小示例：

type FullFilledResults = {
  status: 'fullfilled';
  value: any;
}

type RejectResults = {
  status: 'rejected';
  reason: string;
}

type Results = RejectResults | FullFilledResults

const results: Results[] = [{
  status: 'rejected',
  reason: 'err'
}, {
  status: 'fullfilled',
  value: {}
}]

// Type infer Results[] but I want FullFilledResults[]
const fullfilledResults = results.filter(v => v.status === 'fullfilled')

// Type infer Results[] but I want RejectedResults[]
const rejectedResults = results.filter(v => v.status === 'rejected')

Answer 1

您可以为此使用类型谓词

function assertFullfilled(item: Results): item is FullFilledResults {
    return item.status === 'fullfilled';
}

const fullfilledResults = results.filter(assertFullfilled); // FullFilledResults[]

Answer 2

以下函数对于任何 PromiseSettled 都是通用的

function assertFulfilled<T>(item: PromiseSettledResult<T>): item is PromiseFulfilledResult<T> {
   return item.status === 'fulfilled';
}

Promise.allSettedd打字稿数组推断

2 个答案: