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享元模式是一种优化模式，它最适合解决因创建类似对象而涉及性能的问题。这种模式在js中尤其有用，因为复杂的js代码可能很快就会用光浏览器的所有可用内存。通过把大量独立对象转化为少量共享对象，可降低运行web应用程序所需的资源数量

传统的多实例对象场景

//出厂商、型号、出厂日期、拥有者、车牌号、最近登记日期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('上海大众','迈腾','2012-02-03','bhx','bj0011','2013-04-01'));}var etime = new Date().getTime();alert(etime - stime);

享元模式的改进

//享元模式：优化的设计模式 (优化：时间[代码的运行时间]、空间[web浏览器内存])    //享元模式：内在数据static (出厂商、型号、出厂日期)  外在数据(拥有者、车牌号、最近登记日期)    //出厂商、型号、出厂日期、拥有者、车牌号、最近登记日期    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;        }    };    //工厂模式（闭包工厂）    var CarFactory = (function() {
           //用于承装已经生产好的car         var createdCars = {};        return {            createCar: function(make, model, year) {
                   //如果createdCars对象里已经存在当前的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;                }            }        };    })();    //单体模式(外在的数据 和内在的数据 结合在一起)    var CarRecordManager = (function() {
           //把登记好的汽车放到这个对象里        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('上海大众','迈腾','2012-02-03','bhx','bj0011','2013-04-01'));        //享元模式的测试        // runtime: 300ms   web: 230        arr.push(CarRecordManager.addCarRecord('上海大众', '迈腾', '2012-02-03', 'bhx', 'bj0011', '2013-04-01'));    }    var etime = new Date().getTime();    alert(etime - stime);

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