享元模式是一種優化模式，它最適合解決因建立類似物件而涉及效能的問題。這種模式在js中尤其有用，因為複雜的js程式碼可能很快就會用光瀏覽器的所有可用記憶體。通過把大量獨立物件轉化為少量共享物件，可降低執行web應用程式所需的資源數量

傳統的多例項物件場景

//出廠商、型號、出廠日期、擁有者、車牌號、最近登記日期
var Car = function(make ,model , year , owner , tag , renewDate ){
    this.make = make ; 
    this.model = model ; 
    this.year = year ; 
    this
 
.owner = owner ; 
    this.tag = tag ;
    this.renewDate = renewDate;
};
Car.prototype = {
    constructor:Car  , 
    getMake :function(){
        return this.make;
    },
    getModel:function(){
        return this.model;
    },
    getYear:function(){
        return this.year;
    },
    renewRegistration:function
 
(newRenewDate){
        this.renewDate = newRenewDate;
    }
};

var arr = [] ;

var stime = new Date().getTime();
for(var i = 0 ; i < 5000000; i ++){
    // runtime: 734ms  web: 570
    arr.push(new Car('上海大眾','邁騰','2012-02-03','bhx','bj0011','2013-04-01'));
}
var etime = new Date().getTime();
alert(etime - stime);
 

享元模式的改進

//享元模式：優化的設計模式 (優化：時間[程式碼的執行時間]、空間[web瀏覽器記憶體])
    //享元模式：內在資料static (出廠商、型號、出廠日期)  外在資料(擁有者、車牌號、最近登記日期)


    //出廠商、型號、出廠日期、擁有者、車牌號、最近登記日期
    var Car = function(make, model, year) {
        this.make = make;
        this.model = model;
        this.year = year;
    };
    Car.prototype = {
        constructor: Car,
        getMake: function() {
            return this.make;
        },
        getModel: function() {
            return this.model;
        },
        getYear: function() {
            return this.year;
        }
    };

    //工廠模式（閉包工廠）
    var CarFactory = (function() {
        //用於承裝已經生產好的car 
        var createdCars = {};
        return {
            createCar: function(make, model, year) {
                //如果createdCars物件裡已經存在當前的make ,model , year
                if (createdCars[make + model + year]) {
                    return createdCars[make + model + year];
                } else {
                    var car = new Car(make, model, year);
                    createdCars[make + model + year] = car;
                    return car;
                }
            }
        };
    })();

    //單體模式(外在的資料 和內在的資料 結合在一起)
    var CarRecordManager = (function() {
        //把登記好的汽車放到這個物件裡
        var carRecordDataBase = {};
        return {
            addCarRecord: function(make, model, year, owner, tag, renewDate) {
                var car = CarFactory.createCar(make, model, year);
                carRecordDataBase[tag] = {
                    owner: owner,
                    renewDate: renewDate,
                    car: car
                };
            },
            renewRegistration: function(tag, newRenewDate) {
                carRecordDataBase[tag].renewDate = newRenewDate;
            }
        };
    })();

    var arr = [];

    var stime = new Date().getTime();
    for (var i = 0; i < 5000000; i++) {
        // runtime: 734ms  web: 570
        // arr.push(new Car('上海大眾','邁騰','2012-02-03','bhx','bj0011','2013-04-01'));
        //享元模式的測試
        // runtime: 300ms   web: 230
        arr.push(CarRecordManager.addCarRecord('上海大眾', '邁騰', '2012-02-03', 'bhx', 'bj0011', '2013-04-01'));
    }
    var etime = new Date().getTime();
    alert(etime - stime);