for循环中的Axios不能使用promise，只返回最后一个结果

Question

我正在尝试在 for 循环中发出 axios POST 请求。但是，axios post POST 请求正在运行 n 次，只有循环的最后一个值。以 sheetName="Virudhunagar Beds" 的值运行两次。下面是我的一段代码：

const axios = require('axios')
const sheetDistrictMap = {
  "Ariyalur Beds": "5ea0abd3d43ec2250a483a4f", "Virudhunagar Beds": "5ea0abd3d43ec2250a483a58"
}
let promises = [];

for (sheetName in sheetDistrictMap) {
  promises.push(
    axios.post('https://tncovidbeds.tnega.org/api/hospitals', {
      District: sheetDistrictMap[sheetName],
      FacilityTypes: ["CHO", "CHC", "CCC"],
      IsGovernmentHospital: true,
      IsPrivateHospital: true,
      pageLimit: 100
    })
      .then(res => {
        var outputJsonArray = [];
        for (i = 0; i < res.data.result.length; i++) {
          var rowJson = {};
          var rowdata = res.data.result[i];
          rowJson["Name"] = rowdata["Name"];
          outputJsonArray.push(rowJson);
        }
        console.log("Parsed sheet: " + sheetName);
        console.log(outputJsonArray);
        console.log("========================================================");
      })
      .catch(error => {
        console.error(error)
      })
  )
}
Promise.all(promises).then(() => console.log("All data scraped"));

如何使用每个循环参数进行异步调用？

Answer 1

您遇到了循环内的闭包问题。您可以使用let 和const 关键字来声明sheetName 变量。循环中的每次迭代都会有一个新变量sheetName 具有循环范围。

for (let sheetName in sheetDistrictMap) {
  // the rest code
}

欲了解更多信息，请参阅JavaScript closure inside loops – simple practical example

Answer 2

尝试将const 添加到sheetName 变量中。问题是没有它的变量的行为就像var 在大多数情况下是全局的。添加const 使变量具有块作用域，这样每次迭代都会有一个唯一的变量，而不是使用分配给sheetName 的最后一个值。

for (const sheetName of Object.keys(sheetDistrictMap)) {
  promises.push(
    axios.post('https://tncovidbeds.tnega.org/api/hospitals', {
      District: sheetDistrictMap[sheetName],
      FacilityTypes: ["CHO", "CHC", "CCC"],
      IsGovernmentHospital: true,
      IsPrivateHospital: true,
      pageLimit: 100
    })
      .then(res => {
        var outputJsonArray = [];
        for (i = 0; i < res.data.result.length; i++) {
          var rowJson = {};
          var rowdata = res.data.result[i];
          rowJson["Name"] = rowdata["Name"];
          outputJsonArray.push(rowJson);
        }
        console.log("Parsed sheet: " + sheetName);
        console.log(outputJsonArray);
        console.log("========================================================");
      })
      .catch(error => {
        console.error(error)
      })
  )
}

Answer 3

我认为这里有两件事：

1. let 或 const 在为变量创建全局范围的 for 循环中

2. 您如何从 Promise 中获取数据。将其推送到数组后，您不需要.then，而是这样做：

const axios = require('axios')
const sheetDistrictMap = {
  "Ariyalur Beds": "5ea0abd3d43ec2250a483a4f", "Virudhunagar Beds": "5ea0abd3d43ec2250a483a58"
}
let promises = [];

for (let sheetName in sheetDistrictMap) {
  promises.push(
    axios.post('https://tncovidbeds.tnega.org/api/hospitals', {
      District: sheetDistrictMap[sheetName],
      FacilityTypes: ["CHO", "CHC", "CCC"],
      IsGovernmentHospital: true,
      IsPrivateHospital: true,
      pageLimit: 100
    })
      
  )
}
Promise.all(promises).then((data) => 
   //data will array and in same sequence you hit the api
 // do the below processing for every response
   var outputJsonArray = [];
        for (i = 0; i < res.data.result.length; i++) {
          var rowJson = {};
          var rowdata = res.data.result[i];
          rowJson["Name"] = rowdata["Name"];
          outputJsonArray.push(rowJson);
        }
        //console.log("Parsed sheet: " + sheetName); // make sure you get the sheetName 
        console.log(outputJsonArray);
        console.log("========================================================");
      })
      .catch(error => {
        console.error(error)
      })