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‘);
            };
        }
    }
};