js簡單工廠

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我以計算機為例寫一個簡單原廠模式，只完成加減乘除4個計算功能，考慮到其他功能方便日後擴充，遵循開放-封閉原則。

先看一下C#的簡單工廠是如何?的：

定義抽象類別Operation，加減乘除的實現由子類派生，最後由OperationFactory決定執行個體化哪一個子類。

namespace OperationLibrary{    public abstract class Operation    {        private int num_A = 0;        public int Num_A        {            get { return num_A; }            set { num_A = value; }        }        private int num_B = 0;        public int Num_B        {            get { return num_B; }            set { num_B = value; }        }        public abstract double getResult();    }    public class OperationAdd : Operation    {        public override double getResult()        {            return Num_A + Num_B;        }    }    public class OperationSub : Operation    {        public override double getResult()        {            return Num_A - Num_B;        }    }    public class OperationMul : Operation    {        public override double getResult()        {            return Num_A * Num_B;        }    }    public class OperationDiv : Operation    {        public override double getResult()        {            if (Num_B == 0)                throw new Exception("除數不能為0");            return Num_A / Num_B;        }    }    public class OperationFactory    {        public static Operation createOperate(string operate)        {            Operation oper = null;            switch (operate)            {                case "+":                    oper = new OperationAdd();                    break;                case "-":                    oper = new OperationSub();                    break;                case "*":                    oper = new OperationMul();                    break;                case "/":                    oper = new OperationDiv();                    break;            }            return oper;        }    }}

用戶端調用：

Operation oper = OperationFactory.createOperate("/");oper.Num_A = 6;oper.Num_B = 2;oper.getResult(); //3

 

js類比C#的簡單工廠：

var Operation = function(){        this.num_A = this.num_B = 0;    };    var OperationAdd = function(){};    OperationAdd.prototype = new Operation();    OperationAdd.prototype.getResult = function(){        return this.num_A + this.num_B;    };    var OperationSub = function(){};    OperationSub.prototype = new Operation();    OperationSub.prototype.getResult = function(){        return this.num_A - this.num_B;    };    var OperationMul = function(){};    OperationMul.prototype = new Operation();    OperationMul.prototype.getResult = function(){        return this.num_A * this.num_B;    };    var OperationDiv = function(){};    OperationDiv.prototype = new Operation();    OperationDiv.prototype.getResult = function(){        if(this.num_B == 0)            throw new Error(‘除數不能為0‘);        return this.num_A / this.num_B;    };    var OperateFactory = function(){};    OperateFactory.createOperate = function(operate){        var oper;        switch(operate){            case "+":                oper = new OperationAdd();            break;            case "-":                oper = new OperationSub();            break;            case "*":                oper = new OperationMul();            break;            case "/":                oper = new OperationDiv();            break;        }        return oper;    };        //調用：    var oper = OperateFactory.createOperate(‘+‘);    oper.num_A = 1;    oper.num_B = 2;    alert(oper.getResult()); //3

 

js完全照搬C#的模式顯然太複雜，根據js語言的特性實現一個：

var Operation = function(){        this.num_A = this.num_B = 0;    };    Operation.prototype.OperationAdd = function(){        return this.num_A + this.num_B;    };    Operation.prototype.OperationSub = function(){        return this.num_A - this.num_B;    };    Operation.prototype.OperationMul = function(){        return this.num_A * this.num_B;    };    Operation.prototype.OperationDiv = function(){        if(this.num_B == 0)            throw new Error(‘除數不能為0‘);        return this.num_A / this.num_B;    };   
    //策略    var operateStrategy = {        ‘+‘:‘OperationAdd‘,        ‘-‘:‘OperationSub‘,        ‘*‘:‘OperationMul‘,        ‘/‘:‘OperationDiv‘    };    //工廠    var OperateFactory = (function(){        var oper;        return function(operate){            //只執行個體化一次            oper = oper || new Operation();            return {                setNumber:function(a,b){                    oper.num_A = a;                    oper.num_B = b;                },                getResult:function(){                    var fName = operateStrategy[operate],                        fun = oper[fName] || function(){};                    return fun.call(oper);                }            };        };        })();    //調用：    var oper = OperateFactory(‘+‘);    oper.setNumber(1,3);    alert(oper.getResult());    oper = OperateFactory(‘*‘);    oper.setNumber(2,3);    alert(oper.getResult());

 

總結：如果日後需要擴充計算機的功能，我們需要維護2個地方，一個是為Operation的原型添加所需要的新功能，另一個是維護策略對象：operateStrategy， 基本上不需要修改程式的內部方法，而是為它增加擴充，基本符合開放-封閉原則。

js簡單工廠