[js高手之路]面向对象+设计模式+继承一步步改造简单的四则运算

到目前为止，我已经写完了面向对象完整的一个系列知识，前面基本属于理论，原理的理解，接下来，我们就用学到的知识来实战下吧.

看看理解原理和理论是否重要？例子从简单到复杂

一、单体（字面量）封装加减乘除

            var Oper = {
            add : function( n1, n2 ){
                return n1 + n2;
            },
            sbb : function( n1, n2 ){
                return n1 - n2;
            },
            mul : function( n1, n2 ){
                return n1 * n2;
            },
            div : function( n1, n2 ){
                return n1 / n2;
            },
        };
        console.log( Oper.add( 10, 20 ) ); //30
        console.log( Oper.sbb( 10, 20 ) ); //-10
        console.log( Oper.mul( 10, 20 ) ); //200
        console.log( Oper.div( 10, 20 ) ); //0.5

二、构造函数方式

        function Oper( n1, n2 ){
            this.num1 = n1 || 0;
            this.num2 = n2 || 0;
            this.setData = function( n1, n2 ){
                this.num1 = n1;
                this.num2 = n2;
            };
            this.add = function(){
                this.setData( arguments[0] || this.num1 || 0, arguments[1] || this.num2 || 0 );
                return this.num1 + this.num2;
            };
            this.sbb = function(){
                this.setData( arguments[0] || this.num1 || 0, arguments[1] || this.num2 || 0 );
                return this.num1 - this.num2;
            };
            this.mul = function(){
                this.setData( arguments[0] || this.num1 || 0, arguments[1] || this.num2 || 0 );
                return this.num1 * this.num2;
            };
            this.div = function(){
                this.setData( arguments[0] || this.num1 || 0, arguments[1] || this.num2 || 0 );
                return this.num1 / this.num2;
            };
        };

        console.log( new Oper( 10, 20 ).add() ); //30
        console.log( new Oper(100, 200).sbb( 10, 20 ) ); //-10
        console.log( new Oper().mul( 10, 20 ) ); //200
        console.log( new Oper().div( 10, 20 ) ); //0.5

三、构造函数+原型对象（prototype）

        function Oper(n1, n2) {
            this.num1 = n1 || 0;
            this.num2 = n2 || 0;
        };
        Oper.prototype = {
            constructor : Oper,
            setData : function (n1, n2) {
                this.num1 = n1;
                this.num2 = n2;
            },
            add : function () {
                this.setData(arguments[0] || this.num1 || 0, arguments[1] || this.num2 || 0);
                return this.num1 + this.num2;
            },
            sbb : function () {
                this.setData(arguments[0] || this.num1 || 0, arguments[1] || this.num2 || 0);
                return this.num1 - this.num2;
            },
            mul : function () {
                this.setData(arguments[0] || this.num1 || 0, arguments[1] || this.num2 || 0);
                return this.num1 * this.num2;
            },
            div : function () {
                this.setData(arguments[0] || this.num1 || 0, arguments[1] || this.num2 || 0);
                return this.num1 / this.num2;
            }
        };
        console.log(new Oper().add(10, 20)); //30
        console.log(new Oper( 100, 200 ).sbb()); //-100
        console.log(new Oper().mul(10, 20)); //200
        console.log(new Oper().div(10, 20)); //0.5

四、寄生组合继承+简单工厂模式

        function Oper( n1, n2 ){
            this.num1 = n1;
            this.num2 = n2;
        };
        Oper.prototype.run = function(){}
        function object( o ){
            var G = function(){};
            G.prototype = o;
            return new G();
        };
        function inheritPrototype( subObj, superObj ){
            var proObj = object( superObj.prototype );
            proObj.constructor = subObj;
            subObj.prototype = proObj;
        }

        function OperAdd( n1, n2 ){
            Oper.call( this, n1, n2 );
        }
        inheritPrototype( OperAdd, Oper );
        OperAdd.prototype.run = function(){
            return this.num1 + this.num2;
        }

        function OperSbb( n1, n2 ){
            Oper.call( this, n1, n2 );
        }
        inheritPrototype( OperSbb, Oper );
        OperSbb.prototype.run = function(){
            return this.num1 - this.num2;
        }

        function OperMul( n1, n2 ){
            Oper.call( this, n1, n2 );
        }
        inheritPrototype( OperMul, Oper );
        OperMul.prototype.run = function(){
            return this.num1 * this.num2;
        }

        function OperDiv( n1, n2 ){
            Oper.call( this, n1, n2 );
        }
        inheritPrototype( OperDiv, Oper );
        OperDiv.prototype.run = function(){
            return this.num1 / this.num2;
        }

        function OperFactory( oper, n1, n2 ){
            switch( oper ) {
                case '+':
                    return new OperAdd( n1, n2 ).run();
                break;
                case '-':
                    return new OperSbb( n1, n2 ).run();
                break;
                case '*':
                    return new OperMul( n1, n2 ).run();
                break;
                case '/':
                    return new OperDiv( n1, n2 ).run();
                break;
            }
        }

        console.log( OperFactory( '+', 10, 20 ) ); //30
        console.log( OperFactory( '-', 10, 20 ) ); //-10
        console.log( OperFactory( '*', 10, 20 ) ); //200
        console.log( OperFactory( '/', 10, 20 ) ); //0.5

这种方式，虽然增加了代码量， 如果这道题是实际运用，比如说后面还有很多种运算，两个数的乘方，立方，平方等等，

还有其他特殊处理等等，那么这种扩展性就非常强