Javascript 检查数组，查看它是否在移位后立即为空

所以我在我的音乐机器人上取得了进步。目前，它洗牌播放列表，播放列表中的每首歌曲一次。下一步是让他在播放完每首歌曲后重新洗牌播放列表，然后再继续播放（稍后我会用命令捕捉“阻止”他）。从理论上讲，我所要做的就是加上一个检查“如果数组包含0位置的条目，播放下一首歌”，否则“如果数组为空，再次洗牌播放列表，然后播放下一首歌”

不幸的是，即使下一首歌未定义-检查失败，在播放列表第一次运行之后，他开始滥发未定义的歌曲。我尝试了多种方法来检查这一点。检查数组中的条目是否未定义，检查数组的长度是否未定义，检查条目是否包含在原始歌曲列表中-所有歌曲都存在相同的问题

function PlaySong(connection, channel, SongToPlay) {
        console.log('Now playing '+SongToPlay[0]+'.'); //announce the song
        message.channel.send('Now playing '+SongToPlay[0]+'.');
        const dispatcher = connection.play('./Scythe Digital Edition - Soundtrack/'+SongToPlay[0]+'.mp3'); //play the song
        dispatcher.setVolume(0.1); //at this volume
        dispatcher.on("finish", () => { //when the song concludes
        SongToPlay.shift(); //remove that song from the list of songs to play
            if (!isNullOrUndefined(SongToPlay[0]) || SongToPlay[0] !== '') { //if the list of songs is not empty
                PlaySong(connection, channel, SongToPlay); //repeat the above for the next song
            }
            else { //otherwise if it was empty
                SongToPlay = shuffle(testbells); //shuffle the playlist and repopulate the list of songs to play
                PlaySong(connection, channel, SongToPlay); //then repeat the above for the next song
                //channel.leave();
                //return;
            }
        });
    }

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没有看到所有代码有点困难，所以我制作了一个简单的版本，它应该适合-它只是打印，而不是播放任何东西或消息，但这应该是一个合理的结构为您

//define your starting song array
let originalSongArray = ["Abba","Beatles","ACDC","Britney","Elvis"];

//create a shuffled version of that array 
let shuffledArray = originalSongArray.slice();
shuffle(shuffledArray);

//set the number of songs you want to play 
//note how the number is higher than the array of available songs causing shuffles
let songsToPlay = 12;
while (songsToPlay > 0)
   {
       //"play" the song (in this case write to console)
       console.log("Playing song from, " + shuffledArray[0]);
       //"remove the song from the shuffled list
       shuffledArray.shift();

       //test to ensure there are still songs remaining
       if(shuffledArray.length == 0){
           //regenerate a new shuffled list from the original
           //note, we never altered the original list order or content
           shuffledArray = originalSongArray.slice();
           shuffle(shuffledArray);
       }
   //reduce number of songs to play
   songsToPlay--;
 }

一个简单的洗牌函数引用了这个问题：

function shuffle(array) {
  var currentIndex = array.length, temporaryValue, randomIndex;

  // While there remain elements to shuffle...
  while (0 !== currentIndex) {

    // Pick a remaining element...
    randomIndex = Math.floor(Math.random() * currentIndex);
    currentIndex -= 1;

    // And swap it with the current element.
    temporaryValue = array[currentIndex];
    array[currentIndex] = array[randomIndex];
    array[randomIndex] = temporaryValue;
  }

  return array;
}