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

Brendan Whiting
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Brendan Whiting
Front End Web Development Techdegree Graduate 84,738 Points
Posted by Brendan Whiting
.a{fill-rule:evenodd;}techdegree seal-36
Brendan Whiting
Front End Web Development Techdegree Graduate 84,738 Points

My 'next' button doesn't work.

I've got myself muddled with this one. When I click my next button (or stop button), it doesn't remove the 'current' class on the previous item so it stays pink. It's probably something stupidly obvious.

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();
  }
};

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");

var manOfSteel = new Movie("Man of Steel", 2013, "2:23:00");

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

playlist.add(manOfSteel);

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

playlist.renderInElement(playlistElement);

var playButton = document.getElementById("play");
playButton.onclick = function() {
  playlist.play();
  playlist.renderInElement(playlistElement);  
}

var nextButton = document.getElementById("next");
nextButton.onclick = function() {
  playlist.next();
  playlist.renderInElement(playlistElement);  
}

var stopButton = document.getElementById("stop");
stopButton.onclick = function() {
  playlist.stop();
  playlist.renderInElement(playlistElement);  
}

media.js 

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

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

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

song.js

function Song(title, artist, duration) {
  Media.call(this, title, duration);
  this.artist = artist;
}

Song.prototype = Object.create(Media.prototype);

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;
};

movie.js

function Movie(title, year, duration) {
  Media.call(this, title, duration);
  this.year = year;
}

Movie.prototype = Object.create(Media.prototype);

Movie.prototype.toHTML = function() {
  var htmlString = "<li";
  if (this.isPlaying) {
    htmlString += ' class="current"';
  }
  htmlString += '>';
  htmlString += this.title;
  htmlString += ' (';
  htmlString += this.year;
  htmlString += ') ';
  htmlString += '<span class="duration">';
  htmlString += this.duration;
  htmlString += '</span></li>';
  return htmlString;
  console.log(htmlString);
};

style.css

@import url(http://fonts.googleapis.com/css?family=Varela+Round);
@import url(http://necolas.github.io/normalize.css/3.0.2/normalize.css);

body {
    background: #ECEEEF;
    text-align: center;
    margin: 100px auto;
    width: 80%;
    padding: 0 40px;
    font: 14px normal 'Varela Round', Helvetica, serif;
}

h1 {
    font-size: 20px;
    color:white;
}

div {
    background: #c25975;
    border-radius: 4px;
    border: 1px solid #D5DDE4;
    margin: -40px 0 0;
}

ol {
    list-style-type: none;
    padding: 0;
    background:white;
    margin: 0 0;
    width: 100%;
    display: inline-block;

}

li {
    color: #2C3238;
    width: 96%;
    padding: 15px 2%;
    margin: 0;
    text-align: left;
    border-top: 1px solid #D5DDE4;
}

li span {
    float: right;
    color: #777B7E;
}

li.current {
    background: #ffd7d8;
}

button {
    margin:10px;
    padding:10px 35px;
    border: none;
    border-radius: 5px;
    background: white;

}

index.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="media.js"></script>
    <script src="movie.js"></script>
    <script src="song.js"></script>
    <script src="app.js"></script>

</body>

</html>

1 Answer

elk6
elk6
22,916 Points

Hi Brendan,

It's indeed one small mistake and it's located in your media.js file. Where you wrote:

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

It should have been:

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

Cheers,

Elian