如何使用打字稿中的字符串访问自定义界面的对象属性

Question

我需要使用给定字符串作为键来动态访问我的对象的属性。

我已经检查了以下内容，但找不到我要找的答案：

TypeScript dynamic object properties

错误发生在这里：

state.value[container][id] // TS2571: Object is of type 'unknown'

调用方法 'getEntity' 时，我应该为属性传递一个 ENUM 而不是字符串吗？

下面是我的代码的一个简化示例 - 错误在第 57 行和第 69 行：

// interfaces for entity types - including these in this example seems unnecessary
import {
  TaskFinances,
  Plan,
  Boundary,
  BoundaryMapList
} from 'DTOs'

// for pulling data from REST
import axios, { AxiosResponse } from 'axios'

// VueJS composition AIP components
import { ref } from '@vue/composition-api'

// I want to imply that the State interface below is made up of string:unknown pairs
// so that I can reference it using a string key in the <getEntity> method below

interface Stately {
  [key: string]: unknown
}
interface State extends Stately {
  plans: { [key: number]: Plan };
  taskFinances: { [key: number]: TaskFinances };
  boundaryPointsByField: Boundary[];
}

const props: State = {
  plans: {},
  taskFinances: {},
  boundaryPointsByField: []
}

const state = ref(props)
// I reference the properties of state using state.value.xxx because it is using the Vue3 Composition API Ref syntax

// Reduced to 2 lines following D.R.Y. principles
function getTaskFinances(activityId: number): Promise<TaskFinances> {
  const taskFinances = getEntity(activityId, 'taskFinance', 'taskFinances') as unknown as Promise<TaskFinances>
  return taskFinances
}

// Reduced to 2 lines following D.R.Y. principles
function getBoundaryPointsByField(fieldId: number): Promise<BoundaryMapList> {
  const boundaryPoints = getEntity(fieldId, 'boundaryPointsByField', 'boundaryPointsByField') as unknown as Promise<BoundaryMapList>
  return boundaryPoints
}

// Reduced to 2 lines following D.R.Y. principles
function getPlan(planId: number): Promise<Plan> {
  const plan = getEntity(planId, 'plan', 'plans') as unknown as Promise<Plan>
  return plan
}

// generic method to return requested entities and add them to my state object
async function getEntity(id: number, api: string, container: string): Promise<unknown> {
  try {
    const entity: unknown = state.value[container][id] // THROWS typescript error -TS2571: Object is of type 'unknown'-
    if (entity) {
      return entity
    }
  } catch (err) {
    console.log(container, id, err)
  }

  const url = `${api}${id}`
  try {
    const { data }: AxiosResponse<unknown> = await axios.get(url)
    console.log(api + ':', data)
    state.value[container][id] = data  // THROWS typescript error -TS2571: Object is of type 'unknown'-
    return data
  } catch (err) {
    console.error(err)
  }
}

// interface for my exported uiState object - I use this interface elsewhere in the app so I am exporting it
export interface IUIState {
  getBoundaryPointsByField: (fieldId: number) => Promise<BoundaryMapList>;
  getTaskFinances: (activityId: number) => Promise<TaskFinances>;
  getPlan: (planId: number) => Promise<Plan>;
}

// export my uiState object
export const uiState: IUIState = {
  getBoundaryPointsByField,
  getTaskFinances,
  getPlan
}

Answer 1

此行为是有意的。

你在哪里访问你的状态

 const entity: unknown = state.value[container][id]

state.value[container] 现在是 unknown 类型。您不能尝试访问它后面的 [id]，因为 TS 不知道它是否存在于 state.value[container] 上。这是未知的。这就是使用 unknown 的缺点。如果您知道 API 响应，请为它们创建接口并将它们声明为您的状态的可能类型。否则，如果你想强制它在没有类型的情况下工作，你必须使用 any 而不是 unknown.

您可以看到此行为已重现 here。您可以看到变量 b 的类型是未知的，并且已经抛出错误。如果您在界面中将类型更改为 any，它会起作用，但您不会获得任何类型安全性。

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