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JavaScript Object-Oriented JavaScript (2015) Constructor Functions and Prototypes Making the UI Work

Posted by David Hoffman
David Hoffman
12,707 Points

Help! Uncaught TypeError: Cannot set property 'innerHTML' of null at Playlist.renderInElement (playlist.js:30)

I am having trouble getting the songs to display into the UI. I'm sure I'm missing something small. I've been over the videos 3 times and I cant seem to see what I am doing wrong. Any help would be greatly appreciated. HTML

<!DOCTYPE html>
<html>
<head>
    <title>Treetunes</title>
    <link rel="stylesheet" href="style.css"/>
</head>

<body>

    <div>
        <h1>Treetunes</h1>

        <ol id="playlist">
        </ol>
        <button id="play">Play</button>
        <button id="next">Next</button>
        <button id="stop">Stop</button>

    </div>

    <script src="playlist.js"></script>
    <script src="song.js"></script>
    <script src="app.js"></script>

</body>

</html>

APP.JS

var playlist = new Playlist();

var hereComesTheSun = new Song("Here Comes the Sun", "The Beatles", "2:54");
var walkingOnSunshine = new Song("Walking on Sunshine", "Katrina and the Waves", "3:43");

playlist.add(hereComesTheSun);
playlist.add(walkingOnSunshine);

var playlistElement = document.getElementById("playList");

playlist.renderInElement(playlistElement);

PLAYLIST.JS

function Playlist() {
  this.songs = [];
  this.nowPlayingIndex = 0;
}

Playlist.prototype.add = function(song) {
  this.songs.push(song);
};

Playlist.prototype.play = function() {
  var currentSong = this.songs[this.nowPlayingIndex];
  currentSong.play();
};

Playlist.prototype.stop = function(){
  var currentSong = this.songs[this.nowPlayingIndex];
  currentSong.stop();
};

Playlist.prototype.next = function() {
  this.stop();
  this.nowPlayingIndex++;
  if(this.nowPlayingIndex === this.songs.length){
    this.nowPlayingIndex = 0;
  }
  this.play();
};

Playlist.prototype.renderInElement = function(list) {
  list.innerHTML = "";
  for(var i = 0; i < this.songs.length; i++){
    list.innerHTML += this.songs[i].toHTML();
  }
};

SONG.JS

function Song(title, artist, duration) {
  this.title = title;
  this.artist = artist;
  this.duration = duration;
  this.isPlaying = false;
}

Song.prototype.play = function() {
  this.isPlaying = true;
};

Song.prototype.stop = function() {
  this.isPlaying = false;
};

Song.prototype.toHTML = function() {
 var htmlString = '<li';
 if(this.isPlaying){
   htmlString += ' class="current"';
 }
 htmlString += '>';
 htmlString += this.title;
 htmlString += ' - ';
 htmlString += this.artist;
 htmlString += '<span class="duration">';
 htmlString += this.duration;
 htmlString += '</span></li>';
 return htmlString;
};
David Hoffman
David Hoffman
12,707 Points

I just figured it out. Wow, it must be to early in the morning for this, lol!