使用节点.js,在XMLHttpRequest期间或之后生成新的XMLHttpRequest

我对节点.js和XMLHttpRequest,所以如果这是一个简单回答的问题,请耐心等待。

我目前正在尝试抓取一个朋友的网页(当然是在他的允许下),其中有视频和字幕。我想通过写一个节点.js命令行应用程序。目前,我只是想找到视频的链接和字幕的链接。到目前为止,我得到的是:

#!/usr/bin/env node

var XMLHttpRequest = require("xmlhttprequest").XMLHttpRequest;
var htmlparser = require("htmlparser2");

var xhttp = new XMLHttpRequest();
xhttp.onreadystatechange = function() {
  if (this.readyState == 4 && this.status == 200) {

    // HTML source
    var html = this.responseText;
    var season = 0;
    var episode = 0;

    var parser = new htmlparser.Parser({
      onopentag: function(name, attribs) {
        if (name === "li" && attribs.id === "season-1") {
          season = 1;
          console.log("In season 1");
          for(var attr in attribs){
            console.log(attr);
          }
        }
        if (name === "a" && season === 1) {
          episode = 1;
          var nextPage = attribs.data;
          console.log("\""+nextPage+"\"");

          // Go to "nextPage" here
          xhttp.open("GET", "\""+nextPage+"\"", true);

        }
      },
      onattribute: function(name, value) {
        if(name === "data-url" && season === 1){
          if(value.includes("episode-")){
            episode = value.substr(8,1);
          }
          console.log(value);
          console.log("Episode is: " + episode)
        }
      },
      ontext: function(text) {

      },
      onclosetag: function(tagname) {
        if (tagname === "li" && season === 1) {
          season = 0;
          console.log("Leaving season 1");
        }
      }
    }, {
      decodeEntities: true
    });
    parser.write(html);
    parser.end();

  }
};
xhttp.open("GET", "https://friendspage.org", true);
xhttp.send();

In season 1
id
episode-1
Episode is: 1
"https://friendspage.org/episode-1"
episode-2
Episode is: 2
"https://friendspage.org/episode-2"
episode-3
Episode is: 3
"https://friendspage.org/episode-3"
episode-4
Episode is: 4
"https://friendspage.org/episode-4"
episode-5
Episode is: 5
"https://friendspage.org/episode-5"
episode-6
Episode is: 6
"https://friendspage.org/episode-6"
episode-7
Episode is: 7
"https://friendspage.org/episode-7"
episode-8
Episode is: 8
"https://friendspage.org/episode-8"
episode-9
Episode is: 9
"https://friendspage.org/episode-9"
Leaving season 1

代码按我的要求工作,除了我想转到 nextPage . 我将使用命令行中的输入变量来选择要转到哪个页面,但是目前,我不知道如何转到

// Go to "nextPage" here
xhttp.open("GET", "\""+nextPage+"\"", true);

尝试使用 xhttp.send() send has already been called . 我猜我要么需要关闭当前请求并打开一个新请求,要么只是启动另一个XMLHttpRequest实例。