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JavaScript Design Patterns for Coding Interviews

Challenge: Solution Review

This lesson will explain the solution to the problem from the previous coding challenge.

We'll cover the following...

Solution #

Node.js
class RockMusicVisitor{
    visit(musicLibrary) {
        var rockPlayList=[]; 
        var index = 0;
        var songlist = musicLibrary.songsList.length 
        for(var i=0; i<songlist; i++){
            var song = musicLibrary.songsList[i]
            if(song.getGenre() == "Rock"){
                rockPlayList[index] = song.getName()
                index++
            }
        }
        return rockPlayList
    }
}
class Song{
    constructor(name,genre){
        this.name = name
        this.genre = genre
    }
    getName(){
        return this.name
    }
    getGenre(){
        return this.genre
    }
}
class MusicLibrary{
    constructor(){
        this.songsList = []
    }
    addSong(song){
        this.songsList.push(song)
    }
    accept(visitor){
        return visitor.visit(this)
    }
}
//creating a rock music visitor
var rockmusicVisitor = new RockMusicVisitor()
//creating songs of different genres 
var song1 = new Song("Bohemian Rhapsody","Rock")
var song2 = new Song("Stairway to Heaven","Rock")
var song3 = new Song("Oops I did it again", "Pop")
var song4 = new Song("Crazy", "Country")
//creating a music library
var musicLibrary = new MusicLibrary()
//adding songs to the music library
musicLibrary.addSong(song1)
musicLibrary.addSong(song2)
musicLibrary.addSong(song3)
musicLibrary.addSong(song4)
//using the rockmusicVisitor to create a separate rock music play list
console.log("The music library has the following rock music: " + musicLibrary.accept(rockmusicVisitor))

Explanation

This challenge involved a music library containing different genres of music such as Rock, Pop, and Country. Your task was to implement the visitor pattern to perform the additional operation of creating a separate playlist for the Rock music in the library. We will look into how that is done later on.

Let’s start by discussing the Song class below:

class Song{
    constructor(name,genre){
        this.name = name
        this.genre = genre
    }

    getName(){
        return this.name
    }
    getGenre(){
        return this.genre
    }
}

A Song has the following properties:

  • A ...