Welcome to the Treehouse Community

Want to collaborate on code errors? Have bugs you need feedback on? Looking for an extra set of eyes on your latest project? Get support with fellow developers, designers, and programmers of all backgrounds and skill levels here with the Treehouse Community! While you're at it, check out some resources Treehouse students have shared here.

Looking to learn something new?

Treehouse offers a seven day free trial for new students. Get access to thousands of hours of content and join thousands of Treehouse students and alumni in the community today.

Start your free trial

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

Posted by Ary de Oliveira
Ary de Oliveira
28,298 Points

JavaScript Can't find variable: Song

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);

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);
}

ReferenceError: Can't find variable: Song

1 Answer

Christopher Aporta
Christopher Aporta
24,258 Points

This example is missing constructor functions for the Playlist and Song objects. They would look something like this...

  function Playlist() {
    // ...
  }

  function Song(name) {
    this.name = name
    // ...
  }

These constructors allow you to build instances (e.g. hereComesTheSun) based off of prototypes (e.g. Song) when using the new keyword, a process that forms the foundation for Prototypal Inheritance & Object-Oriented JavaScript.