for循环内有2个ajax调用

Question

I have created a web page that interacts with the Twitch API. The app basically shows a twitch user's name, logo and whether they are offline or online.

To do this. I did two AJAX calls:

  var twitches = [
    "freecodecamp",
    "orb",
    "medrybw",
    "storbeck",
    "terakilobyte",
    "habathcx",
    "RobotCaleb",
    "thomasballinger",
    "noobs2ninjas",
    "beohoff"
  ];

  // Retrieve the username and logo of the user
for(x=0;x < twitches.length; x++){
      $.ajax({
        url:"https://api.twitch.tv/kraken/users/"+ twitches[i] + "?client_id=fmg7qm7vtgxozyr7dj2icwrumdb186",
        type: "GET",
        dataType: "jsonp",
        success: function(x) {
          if (x.logo == null) {
            x.logo =
              "http://www.dotcomsolicitors.com/wp-content/uploads/sites/491/2017/08/user-icon-300x300.png";
          }
          $(".tbody").append(
            "<tr><td>" +
              '<a href="https://go.twitch.tv/' +
              x.name +
              '">' +
              '<img src="' +
              x.logo +
              '"/></a></td><td><p>' +
              '<a href="https://go.twitch.tv/' +
              x.name +
              '">' +
              x.name +
              '</a></p></td><td class="onOroff"></td></tr>'
          );
        }
      });
}

and this AJAX call checks whether the user is online or not. If x.stream === null this means the user is offline, so a no sign will be appended to the last column. But there seems to a problem with my loop and I don't know how to fix it. The codepen is https://codepen.io/mrsalami/pen/yPaOqO .

for(x=0;x < twitches.length; x++){
$.ajax({
    url:"https://api.twitch.tv/kraken/streams/"+ twitches[i] + "?client_id=fmg7qm7vtgxozyr7dj2icwrumdb186",
    type: "GET",
    dataType: "jsonp",
    success: function(x) {
      console.log(x.stream);

      if (x.stream === null) {
        $(".onOroff").append(
          '<img src="https://upload.wikimedia.org/wikipedia/commons/thumb/d/d5/No_sign.svg/300px-No_sign.svg.png" alt="Image result for no symbol png"/>');
      } else {
        $(".onOroff").append(
          '<img src="https://www.shareicon.net/download/2015/10/24/136117_ok_300x300.png" alt="Image result for yes symbol png"/>'
        );
      }
    }
  });

}

Console Log:

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Object {
  _id: 26678888912,
  _links: Object {
    self: "https://api.twitch.tv/kraken/streams/medrybw"
  },
  average_fps: 24.025974026,
  channel: Object {
    _id: 50332395,
    _links: Object {},
    background: null,
    banner: null,
    broadcaster_language: "en",
    created_at: "2013-10-18T22:13:12Z",
    delay: null,
    display_name: "MedryBW",
    followers: 23013,
    game: "StarCraft",
    language: "en",
    logo: "https://static-cdn.jtvnw.net/jtv_user_pictures/medrybw-profile_image-19fce7e1b0d6c194-300x300.jpeg",
    mature: false,
    name: "medrybw",
    partner: false,
    profile_banner: null,
    profile_banner_background_color: "",
    status: "24/7 Classic Starcraft VoD stream 2000-2012 (6344 VoDs)",
    updated_at: "2017-11-08T08:33:30Z",
    url: "https://www.twitch.tv/medrybw",
    video_banner: null,
    views: 854932
  },
  created_at: "2017-11-08T04:26:27Z",
  delay: 0,
  game: "StarCraft",
  is_playlist: false,
  preview: Object {
    large: "https://static-cdn.jtvnw.net/previews-ttv/live_user_medrybw-640x360.jpg",
    medium: "https://static-cdn.jtvnw.net/previews-ttv/live_user_medrybw-320x180.jpg",
    small: "https://static-cdn.jtvnw.net/previews-ttv/live_user_medrybw-80x45.jpg",
    template: "https://static-cdn.jtvnw.net/previews-ttv/live_user_medrybw-{width}x{height}.jpg"
  },
  stream_type: "live",
  video_height: 768,
  viewers: 22
}

​
Object {
  _id: 26669328176,
  _links: Object {
    self: "https://api.twitch.tv/kraken/streams/orb"
  },
  average_fps: 60,
  channel: Object {
    _id: 20519306,
    _links: Object {},
    background: null,
    banner: null,
    broadcaster_language: "en",
    created_at: "2011-02-17T07:14:53Z",
    delay: null,
    display_name: "Orb",
    followers: 166319,
    game: "Call of Duty: WWII",
    language: "en",
    logo: "https://static-cdn.jtvnw.net/jtv_user_pictures/orb-profile_image-076d545e806d2190-300x300.png",
    mature: false,
    name: "orb",
    partner: true,
    profile_banner: "https://static-cdn.jtvnw.net/jtv_user_pictures/0e56159f562dcf9f-profile_banner-480.png",
    profile_banner_background_color: "",
    status: "24/7 Race to Prestige 🏆 Annual Call of Duty Marathon | OFFICIAL !Merch 🔥 | !DXRacer Giveaway | Powered by: !Elgato !Razer !Nvidia",
    updated_at: "2017-11-08T08:33:25Z",
    url: "https://www.twitch.tv/orb",
    video_banner: "https://static-cdn.jtvnw.net/jtv_user_pictures/orb-channel_offline_image-0d0763efc52d70f3-1920x1080.png",
    views: 16628568
  },
  created_at: "2017-11-06T22:45:13Z",
  delay: 0,
  game: "Call of Duty: WWII",
  is_playlist: false,
  preview: Object {
    large: "https://static-cdn.jtvnw.net/previews-ttv/live_user_orb-640x360.jpg",
    medium: "https://static-cdn.jtvnw.net/previews-ttv/live_user_orb-320x180.jpg",
    small: "https://static-cdn.jtvnw.net/previews-ttv/live_user_orb-80x45.jpg",
    template: "https://static-cdn.jtvnw.net/previews-ttv/live_user_orb-{width}x{height}.jpg"
  },
  stream_type: "live",
  video_height: 864,
  viewers: 624
}
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Answer 1

Basically your code is one big race condition. In one ajax callback you create a table cell and in the other you try to append something to an empty cell. If the first returns before the second then all should work. If not, there is no empty cell yet for the second to append to.

Reorganise your code to use Promises, and use Promise.all to wait for both to return. Once that happens you can create your content all in one place.

Something like this.

var twitches = [...];// your array
for(var i=0;i<twitches.length;i++){
    Promise.all([
        $.ajax(...),  // first ajax call, without the success callback
        $.ajax(...)   // second ajax call, without the success callback
    ]).then(function(results){
       var usernameAndLogoResult = results[0];
       var statusResult = results[1];
       // build your html here
    });
}