javascript设计模式2

接口：利 固化一部分代码 弊 丧失js的灵活性

在JavaScript中模仿接口

/*

interface Composite{

    function add(child);

    function remove(child);

    function getChild(index);

}

interface FormItem{

    function save();

}

*/

var CompositeForm=function(id,method,action){

    ...

};

CompositeForm.prototype.add = function(child) {

    ...

};

CompositeForm.prototype.remove = function(child) {

    ...

};

CompositeForm.prototype.getChild = function(index) {

    ...

};

CompositeForm.prototype.save = function() {

    ...

};

改进一下，用属性检查

/*

interface Composite{

    function add(child);

    function remove(child);

    function getChild(index);

}

interface FormItem{

    function save();

}

*/

var CompositeForm=function(id,method,action){

    this.implementsInterfaces=['Composite','FormItem'];

    ...

};

...

function addForm(formInstance){

    if (!implements(formInstance,'Composite','FormItem')) {

        throw new Error("Object does not implement a required interface.");

    }

    ...

}

function implements(Object){

    for(var i=1;i<arguments.length;i++){

        var interfaceName=arguments[i];

        var interfaceFound=false;

        for(var j=0;j<Object.implementsInterfaces.length;j++){

            if (Object.implementsInterfaces[j]==interfaceName) {

                interfaceFound=true;

                break;

            };

        }

        if (!interfaceFound) {

            return false;

        };

    }

    return true;

}

用鸭式辨型模仿接口

var Composite =new Interface('Composite',['add','remove','getChild']);

var FormItem=new Interface('FormItem',['save']);

var CompositeForm=function(id,method,action){

    ...

};

...

function addForm(formInstance){

    ensureImplements(formInstance,Composite,FormItem);

    ...

}

结合第一种和第三种

 

var Composite =new Interface('Composite',['add','remove','getChild']);

var FormItem=new Interface('FormItem',['save']);

var CompositeForm=function(id,method,action){

    ...

};

...

function addForm(formInstance){

    Interface.ensureImplements(formInstance,Composite,FormItem);

    ...

}

Interface类的定义

var Interface=function(name,method){

    if(arguments.length!=2){

        throw new Error("需要2个参数");

    }

    this.name=name;

    this.method=[];

    for(var i=0,len=methods.length;i<len;i++){

        if(typeof methods[i]=='string'){

            throw new Error("需要是一个字符串");

        }

        this.methods.push(methods[i]);

    }

};

Interface.ensureImplements=function(object){

    if(arguments.length<2){

        throw new Error("至少需要2个参数");

    }

    for(var i=1,len=arguments.length;i<len;i++){

        var interface=arguments[i];

        if(interface.constructor!=Interface){

            throw new Error("需要2个参数，并是Interface的实例");

        }

        for(var j=0,methodsLen=interface.methods.length;j<methodsLen;j++){

            var method=interface.methods[j];

            if (!object[method]||typeof object[method]!=='function') {

                throw new Error('方法未找到');

            };

        }

    }

};