JavaScript对象是emtpy

我正在使用SpotifyAPI转储用户的所有播放列表和包含的曲目名称。我知道了如何请求该信息，并尝试将其存储在一个散列中，在该散列中，可以通过播放列表名称散列[playlist name]=[track1，track2，等等]找到一组曲目。当我将console.log记录下来时，一切看起来都很好

但是，当我尝试使用handle bars帮助程序迭代并显示所有内容时，JavaScript认为对象是空的。下面是一些代码：

//helper that will display eventually, but right now logs "undefined"
Handlebars.registerHelper('read_hash', function(hash){
    console.log(hash.length); //undefined
    console.log(Object.keys(hash); //undefined
    console.log(hash); //looks fine.. results in screenshot..
});

//ajax request that successfully get's all of the playlist data I want
        $.ajax({
            url: 'https://api.spotify.com/v1/me/playlists',
            headers: {
              'Authorization': 'Bearer ' + access_token
            },
            success: function(response) {
              //make a new hash and put in template
              var processed = 0;
              response.items.forEach(function(e){
                var playlistName = e.name;
                //get tracks by nesting a request lol
                $.ajax({
                  url: e.tracks.href,
                  headers: {
                    'Authorization': 'Bearer ' + access_token
                  },
                  success: function(responseTwo) { //returns track objects
                    playlists[playlistName] = responseTwo.items;
                    processed++;
                  }
                }).done(function(){
                  if(processed >= response.items.length)
                  {
                    playlistPlaceholder.innerHTML = playlistTemplate({Playlists: playlists}); //get playlists
                  }
                });
              });

//handle bars template with call to read_hash
<script id="playlist-template" type="text/x-handlebars-template">
  <h1>playlists</h1>
  <table>
    <tr>
      <th>playlist</th>
      <th>tracks</th>
    </tr>
    {{read_hash Playlists}}
  </table>
</script>

---

另外，当我从read_hash控制台记录JSON.stringifyhash时，我会得到我想要的结果，所以。。。也许有些东西起作用了

长度属性仅适用于数组，响应是一个对象

 var property = {"test object track 123":"test"};
 console.log(property.length); //shows undefined

此外，registerHelper语句必须生成错误，因为没有闭合括号 迭代属性

//show error "closed parenthesis"
console.log(Object.keys(hash); //undefined

//helper that will display eventually, but right now logs "undefined"
Handlebars.registerHelper('read_hash', function(hash){
        for (var playlist in hash) {
            console.log("the length of item is" + hash[playlist].length);
        }
});

---

我通过使用ajaxdone回调修复了它。也许有一种更有条理的方法来处理这个问题，但我的解决方案是：

转储播放列表数据的ajax请求：

$.ajax({
    url: 'https://api.spotify.com/v1/me/playlists',
    headers: {
      'Authorization': 'Bearer ' + access_token
    },
    success: function(response) {
      //make a new hash and put in template
      var processed = 0;
      response.items.forEach(function(e){
        var playlistName = e.name;
        //get tracks by nesting a request lol
        $.ajax({
          url: e.tracks.href,
          headers: {
            'Authorization': 'Bearer ' + access_token
          },
          success: function(responseTwo) { //returns track objects
            playlists[playlistName] = responseTwo.items;
            processed++;
          }
        }).done(function(){
          if(processed >= response.items.length)
          {
            playlistPlaceholder.innerHTML = playlistTemplate({Playlists: playlists}); //get playlists
          }
        });
      });
      //console.log(playlists);
      $('#login').hide();
      $('#loggedin').show();
    }
});

用于分析关联数组的把手辅助对象：

Handlebars.registerHelper('read_hash', function(hash){
  jsonHash = JSON.parse(JSON.stringify(hash));
  var html = "<table style='width:5px'><tr><th>Playlist</th><th>Track</th></tr>"; //stores markup to write and return at end
  for(var playlistName in jsonHash)
  {
    var playlistTracks = jsonHash[playlistName];
    html = html + "<tr><td>" + playlistName + "</td><td><ul>";
    for(var i = 0; i < playlistTracks.length; i++)
    {
      html =  html + "<li>" + playlistTracks[i].track.name + "</li>";
    }
    html = html + "</ul></td></tr>";
  }
  console.log(html + "</table>");
  return new Handlebars.SafeString(html + "</table>");
});

要显示的把手模板：

<script id="playlist-template" type="text/x-handlebars-template">
  <h1>playlists</h1>
  {{read_hash Playlists}}
  <table>
    <tr>
      <th>playlist</th>
      <th>tracks</th>
    </tr>
  </table>
</script>

---

read_hash调用在哪里？您试图在填充对象之前访问该对象，控制台显示{}.$这一事实就很明显了。ajax是异步的。playlists[playlistName]=responseTwo.items；在playlipholder.innerHTML=playliptemplate{Playlists:Playlists}；之后发生；。还请注意蓝色的小i框。这可能是控制台中延迟加载的一个典型案例，使您认为它已定义。console.logJSON.stringifyhash；值得一提的是，JavaScript没有散列类型，对象也没有实现为真正的散列表。您可能需要记录哈希类型，以查看实际使用的内容。请查看。它也可以通过数组来完成。