可变大小循环内的http请求，只有在最后一个请求完成后才能做某事（JavaScript）

Question

我正在使用 request 在可变大小的循环中发出 HTTP 请求。 （我将从文件中读取单词，现在我只有一个数组）。 我在每个循环中添加一个对象（响应），并且只想在最后一个请求完成后返回该对象。 我一直在玩承诺，但我不确定如何链接它们，因为它是可变数量的请求。

const request = require('request');

// eventually this array will be populated by reading a file
var words = ["hello", "there"];
var response = {};

// Loop thruogh input string
for (var i = 0; i < words.length; i += 1) {
    // get next word
    var curWord = words[i];
    // if the current word is not already in the response
    if (!(curWord in response)) {
        // request info from dictionary
        var options = {
            url: 'https://api.dictionaryapi.dev/api/v2/entries/en/' + curWord,
            json: true
        }
        request(options, (err, res, body) => {
            if (err) { return console.log(err); }            
            // find part of speech 
            var partOfSpeech;
            try {
                partOfSpeech = body[0].meanings[0].partOfSpeech
            } catch (err) {
                partOfSpeech = "undefined";
            }  
            // add to response          
            response[curWord] = partOfSpeech;
        });

    }
      
}
// do this part only after last request has been completed
console.log(response);

Answer 1

基本上，您需要计算响应，知道当计数器达到零时，您就完成了所有响应。

const request = require('request');

var words = ["hello", "there"];
var response = {};

var count = words.length;

for (var i = 0; i < words.length; i += 1) {
  var curWord = words[i];

  if (!(curWord in response)) {
    var options = {
      url: 'https://api.dictionaryapi.dev/api/v2/entries/en/' + curWord,
      json: true
    }
    request(options, (err, res, body) => {
      count--

      if (err) {
        return console.log(err);
      }
      // find part of speech 
      var partOfSpeech;
      try {
        partOfSpeech = body[0].meanings[0].partOfSpeech
      } catch (err) {
        partOfSpeech = "undefined";
      }
      // add to response          
      response[curWord] = partOfSpeech;

      if (count == 0) {
        // do this part only after last request has been completed
        console.log(response);
      }
    });

  }

}