Flyweight

A fine-grained instance used for efficient sharing

• Flyweight pattern is used when there is a need to create a large number of objects of almost similar nature.

• The large number of objects consume a large amount of memory and the flyweight design pattern provides a solution for reducing the load on memory by sharing objects.

• It is primarily used to reduce the number of object creation, to reduce memory footprints and increase performance.

• This pattern tries to reuse the existing similar kind of object by storing them and creates new object when no matching object is found.

• Most frequently used in JavaScript.

EX:
function Flyweight (make, model, processor) {
    this.make = make;
    this.model = model;
    this.processor = processor;
};
 
var FlyWeightFactory = (function () {
    var flyweights = {}; 
    return { 
        get: function (make, model, processor) {
            if (!flyweights[make + model]) {
                flyweights[make + model] = 
                    new Flyweight(make, model, processor);
            }
            return flyweights[make + model];
        }, 
        getCount: function () {
            var count = 0;
            for (var f in flyweights) count++;
            return count;
        }
    }
})();
 
function ComputerCollection () {
    var computers = {};
    var count = 0; 
    return {
        add: function (make, model, processor, memory, tag) {
            computers[tag] = 
                new Computer(make, model, processor, memory, tag);
            count++;
        }, 
        get: function (tag) {
            return computers[tag];
        }, 
        getCount: function () {
            return count;
        }
    };
}
 
var Computer = function (make, model, processor, memory, tag) {
    this.flyweight = FlyWeightFactory.get(make, model, processor);
    this.memory = memory;
    this.tag = tag;
    this.getMake = function () {
        return this.flyweight.make;
    }
}

var computers = new ComputerCollection();
computers.add("Dell", "Studio XPS", "Intel", "5G", "Y755P");
computers.add("Dell", "Studio XPS", "Intel", "6G", "X997T");
computers.add("Dell", "Studio XPS", "Intel", "2G", "U8U80");
computers.add("Dell", "Studio XPS", "Intel", "2G", "NT777");
computers.add("Dell", "Studio XPS", "Intel", "2G", "0J88A");
computers.add("HP", "Envy", "Intel", "4G", "CNU883701");
computers.add("HP", "Envy", "Intel", "2G", "TXU003283");

console.log("Computers: " + computers.getCount()); // 7
console.log("Flyweights: " + FlyWeightFactory.getCount()); // 2