flyweight pattern

flyweight.js

// Flyweight Pattern
/*
    Here we are sharing a part of our data into a separate object.
 */


 (function() {
    'use strict';

    // Usual constructor method 
    function Book(data) {
        this.flyweight = BookFlyweight.get(data.genres, data.language, data.ratings, data.types);
        this.name = data.name;
        this.author = data.author;
    }

    var BookFlyweight = function() {
        var flyweights = {};
        var get = function(genres, language, ratings, types) {
            if (!flyweights[genres+language+ratings+types]) {
                flyweights[genres+language+ratings+types] = 
                    new Flyweight(genres,language,ratings,types);
            }
            return flyweights[genres+language+ratings+types];
        }
        var getCount = function() {
            var count = 0;
            for (var c in flyweights) { 
                count++;
            }
            return count;
        }
        return {
            get: get,
            getCount: getCount,
        }
    }()

    /*
    These are the shared values.
     */
    function Flyweight(genres, language, ratings, types) {
        this.genres = genres; 
        this.language = language; 
        this.ratings = ratings; 
        this.types = types;
    }

    var BookCollection = function() {
        var books = {}, count = 0;
        var add = function(data) {
            books[data.name] = new Book(data);
            count++;
        }
        var getCount = function() {
            return count;
        }
        return {
            add: add,
            getCount: getCount,
        }
    }

    

    var books = new BookCollection();
    // Defining the limits of shared data.
    var genres = [ 'mystery', 'fantasy', 'romance', 'sci-fi'];
    var language = [ 'Eng', 'Fre', 'Spa', 'Jp', 'Others'];
    var ratings = [ '1', '2', '3', '4', '5']; 
    var types = [ 'AudioBook', 'Ebook', 'Print'];

    for (var i = 0; i < 10000; i++) {
        books.add({
            name: 'book'+i,
            author: 'author'+i,
            genres : genres[Math.floor((Math.random() * 4))], 
            language : language[Math.floor((Math.random() * 5))], 
            ratings : ratings[Math.floor((Math.random() * 5))], 
            types : types[Math.floor((Math.random() * 3))]
        });
    }
    console.log(books.getCount()); // 10000
    console.log(BookFlyweight.getCount()); // 300 
    
    /*
    BookFlyweight.getCount() will give the number of shared 
    flyweight that these records have. for 1000 we get 300 
    flyweight at random. With increased complexity this technique
    can really increase efficiency.
     */
    

})();