无法执行 .map whithin 功能 [英] Unable to perform .map whithin function

问题描述

背景

我正在构建一个 React-Redux 应用程序，它必须处理一些对私有 API 的 axios 调用.所述 API 不在我的控制之下，我无法修改任何内容.其中一个 axios 请求由一个函数执行，我们称之为getData".这个请求使用 POST 作为它的方法并且需要一个参数category"，它一次只接受一个值.有时我需要一次执行三个请求，我打算以编程方式执行此操作，而不是为每个可能的请求硬编码一个请求，因为可用类别的数量很多.

我打算构建什么

一个执行请求的函数，它接受两个参数，一个是令牌，另一个是作为类别"传递的可能值数组.参数.该函数应该为数组中的每个值运行一次，并返回一个包含所有产品"的对象数组.从后端带来.

我已经构建的

export const getData = (tk, values) =>价值观.map(值=>apiInstance.request({网址:ENDPOINTS.ENDPOINT，方法:'POST'，数据:qs.stringify({令牌:令牌，类别:价值，}),}),).then(响应 => {返回 response.data;}).catch(错误=> {返回 Promise.reject(error.message);});

以上是实际请求，接下来是 redux 操作:

export const actionTypes = keyMirror({RETRIEVE_REQUEST:空，RETRIEVE_SUCCESS:空，RETRIEVE_FAILURE:空，});const actionCreators = {请求:createAction(actionTypes.RETRIEVE_REQUEST)，成功:createAction(actionTypes.RETRIEVE_SUCCESS)，失败:createAction(actionTypes.RETRIEVEO_FAILURE)，};export constretrieveData = (tk, values) =>调度 =>{调度(actionCreators.request())；Promise.all(getData(tk, values)).then(data => dispatch(actionCreators.success(data))).catch(error => dispatch(actionCreators.failure(error)));};

还有减速器:

export const initialState = {加载:假，数据: []，错误:空，};const 动作映射 = {[actionTypes.RETRIEVE_REQUEST]:状态 =>({...状态，加载:真实，}),[actionTypes.RETRIEVE_SUCCESS]:(状态，动作)=>({...状态，加载:假，数据:action.payload，}),[actionTypes.RETRIEVE_FAILURE]:(状态，动作)=>({...状态，加载公共:假，错误:action.payload，}),};导出默认值(状态 = 初始状态，动作)=>{const actionHandler = actionsMap[action.type];如果(！actionHandler){返回状态；}返回 actionHandler(state, action);};

<块引用>

请注意，所有这些都在单独的文件中.

问题

我收到错误消息 undefined is not a function (near '...}).then(function (response)...') 这指向 values.map((值) =>

问题

据我所知，.map 可以接收一个像这样的短箭头函数作为它的第一个参数.Values 是一个字符串数组，所以理论上它应该可以工作.我错过了什么?

解决方案

问题在于您将 values 映射到 Promise 列表.

但是，在您的情况下，.then() 不能在列表 ([Promise, Promise, ...]) 上调用.事实上， .then 将是 undefined 这正是错误消息告诉你的.

相反，尝试将 values.map(...) 包装在 Promise.all(...) 中.这将在调用 .then(...) 之前等待所有 promise 得到解决.

请记住，传递给 .then(...) 的 response 实际上也是一个列表！

所以你想做这样的事情:

Promise.all(价值观.map(值=>apiInstance.request({网址:ENDPOINTS.ENDPOINT，方法:'POST'，数据:qs.stringify({令牌:令牌，类别:价值，}),}),)).then(响应 => {//响应是一个列表！返回 response.map(response => response.data);}).catch(错误=> {返回 Promise.reject(error.message);});

Background

I'm building a React-Redux application which, amongst other things, has to handle some axios calls to a private API. Said API is not under my control, and I cannot modify anything. One of the axios requests is performed by a function, let's call it "getData". This request uses POST as its method and requires a parameter "category", this accepts only one value at a time. Thing is sometimes I need to perform say three requests at a time and I intend to do so programatically rather than hardcoding a request for each possible request, as the number of available categories is high.

What I intent to build

A function which performs a request, taking in two parameters, one is a token, the other one is an array of possible values to be passed as the "category" param. The function should run once per value in the array and return a single array of objects which holds all of the "products" brought over from the backend.

What I've built already

export const getData = (tk, values) =>
  values
    .map(value =>
      apiInstance.request({
        url: ENDPOINTS.ENDPOINT,
        method: 'POST',
        data: qs.stringify({
         token: token,
         category: value,
        }),
      }),
    )
    .then(response => {
      return response.data;
    })
    .catch(error => {
      return Promise.reject(error.message);
    });

Above is the actual request and next is the redux action:

export const actionTypes = keyMirror({
  RETRIEVE_REQUEST: null,
  RETRIEVE_SUCCESS: null,
  RETRIEVE_FAILURE: null,
});

const actionCreators = {
  request: createAction(actionTypes.RETRIEVE_REQUEST),
  success: createAction(actionTypes.RETRIEVE_SUCCESS),
  failure: createAction(actionTypes.RETRIEVEO_FAILURE),
};

export const retrieveData = (tk, values) => dispatch => {
  dispatch(actionCreators.request());
  Promise.all(getData(tk, values))
    .then(data => dispatch(actionCreators.success(data)))
    .catch(error => dispatch(actionCreators.failure(error)));
};

And the reducer:

export const initialState = {
  loading: false,
  data: [],
  error: null,
};

const actionsMap = {
  [actionTypes.RETRIEVE_REQUEST]: state => ({
    ...state,
    loading: true,
  }),

  [actionTypes.RETRIEVE_SUCCESS]: (state, action) => ({
    ...state,
    loading: false,
    data: action.payload,
  }),

  [actionTypes.RETRIEVE_FAILURE]: (state, action) => ({
    ...state,
    loadingPublic: false,
    error: action.payload,
  }),
};

export default (state = initialState, action) => {
  const actionHandler = actionsMap[action.type];
  if (!actionHandler) {
    return state;
  }
  return actionHandler(state, action);
};

Note that all of these are in separate files.

Problem

I'm getting the error message undefined is not a function (near '...}).then(function (response)...') and this points to values.map((value) =>

Question

As far as I understand, .map can recieve a short-arrow function such as this as its first parameter. Values is an array of strings, so it should work in theory. What am I missing?

解决方案

The problem is that you map your values to a list of Promises.

However, .then() is not callable on a list ([Promise, Promise, ...]) in your case. In fact, .then will be undefined which is exactly what the error message tells you.

Instead, try to wrap values.map(...) in a Promise.all(...). This will wait for all promises to resolve before calling .then(...).

Keep in mind that the response passed to .then(...) will actually also be a list!

So you want to do something like this:

Promise.all(
  values
    .map(value =>
      apiInstance.request({
        url: ENDPOINTS.ENDPOINT,
        method: 'POST',
        data: qs.stringify({
         token: token,
         category: value,
        }),
      }),
    )
)
.then(responses => {
  // responses is a list!
  return responses.map(response => response.data);
})
.catch(error => {
  return Promise.reject(error.message);
});

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