javascript设计模式一——接口

JavaScript是弱类型语言，所以类型匹配问题很难追踪。同时，Js并没有像其他语言一样，提供内置的创建或实现接口的方法。这样，在我们进行对象转化的时候是很困难的。

不过，我们还是可以使用程序来模拟JavaScript Interface接口的实现。一般来说，模拟Interface的实现有如下三种方法：

注释法——将接口的定义写在注释中，大家能否小心注意，以实现接口的所有方法全凭自觉。

java中使用interface和implements关键字实现接口的

/*
interface Composite{
	function add(child);
	function remove(child);
	function getChild(index);
}

interface FormItem{
	function save();
}
*/

//模拟CompositeForm继承了Composite、FormItem接口
var CompositeForm = function(id,name,action){
	...
}

CompositeForm.prototype = {
	add:function(child){
		...
	},
	remove:function(child){
		...
	},
	getChild:function(index){
		...
	},
	save:function(){
		...
	}
}

备注：这种模仿并不是很好，它没有为确保CompositeForm真正实现了正确的方法集而进行检查，也不会抛出错误以告知程序中有问题。

属性检查法——自己说明我实现了哪些接口，一会儿你检查的时候记得检查我说我实现的接口里面，是否把我真正想要实现的接口全部实现了（这么别扭呢），总之就是自欺欺人

var CompositeForm = function(id, method, action) {
    //声明自己继承了Composite，FormItem接口
    this.implementsInterfaces = ['Composite', 'FormItem'];
   ...
};

function addForm(formInstance) {
    //判断formInstance是否继承了Composite，FormItem接口
    if(!implements(formInstance, 'Composite', 'FormItem')) {
        throw new Error("Object does not implement a required interface.");
    }
    ...
}

//判断当前对象是否继承了对象声明的接口
function implements(object) {
    for(var i = 1; i < arguments.length; i++) { // Looping through all arguments 
                                                // after the first one.
        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; // An interface was not found.
        }
    } 	
    return true; // All interfaces were found.
}

鸭式辨型法——如果对象具有与接口定义的方法同名的所有方法，那么久可以认为它实现了这个接口。

var Interface = function(name,methods){
	if(arguments.length!=2){
		throw new Error("Interface 的构造函数一定只能有两个参数")
	}
	this.name = name;
	this.methods = [];
	
	for(var i=0,len=methods.length;i<len;i++){
		if(typeof methods[i] !== "string"){
			throw new Error("Interface构造参数方法名称为string类型");
		}else{
			this.methods.push(methods[i]);
		}
	}
}

Interface.ensureImplements = function(object){
	//至少包含两个参数——继承接口的对象，对应的接口（至少含有一个）
	if(arguments.length<2){
		throw new Error("Function Interface.ensureImplements called with " + 
          arguments.length  + "arguments, but expected at least 2.");
	}
	
	for(var i=1,len=arguments.length;i<len;i++){
		//具体实现接口的对象
		var _interface = arguments[i];
		if(_interface.constructor !== Interface) {
            throw new Error("Function Interface.ensureImplements expects arguments "   
              + "two and above to be instances of Interface.");
        }
		
		//接口对应的参数
		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("Function Interface.ensureImplements: object " 
                  + "does not implement the " + _interface.name 
                  + " interface. Method " + method + " was not found.");
            }
		}
		
	}
	
	
}

var Composite = new Interface("Composite",["add","remove","getChild"]);
var FormItem = new Interface("FormItem",["save"]);

//CompositeForm继承Composite、FormItem两个接口

/*提示缺少接口对象参数
var CompositeForm = new function(id, method, action){
}
Interface.ensureImplements(CompositeForm);
*/

/*提示没有实现Composite接口
var CompositeForm = new function(id, method, action){
}
Interface.ensureImplements(CompositeForm,Composite);
*/

/*提示没有实现Composite接口
var CompositeForm = new function(id, method, action){
	this.add=function(){};
	this.remove=function(){};
	//this.getChild=function(){};
}
Interface.ensureImplements(CompositeForm,Composite);
*/

/*正确显示
var CompositeForm = new function(id, method, action){
	this.add=function(){};
	this.remove=function(){};
	this.getChild=function(){};
}
Interface.ensureImplements(CompositeForm,Composite);
*/

/*
var CompositeForm = new function(id, method, action){
	this.add=function(){};
	this.remove=function(){};
	this.getChild=function(){};
	this.save=function(){};
}
Interface.ensureImplements(CompositeForm,Composite,FormItem);
*/

var CompositeForm = new function(id, method, action){
	this.add=function(){};
	this.remove=function(){};
	this.getChild=function(){};
	this.save=function(){};
	//用来验证当前对象是否实现了Composite,FormItem接口
	Interface.ensureImplements(this,Composite,FormItem);
}

 教程上的另外一个例子

ResultFormatter.prototype.renderResults = function() {
  var dateOfTest = this.resultsObject.getDate();
  var resultsArray = this.resultsObject.getResults();
  
  var resultsContainer = document.createElement('div');

  var resultsHeader = document.createElement('h3');
  resultsHeader.innerHTML = 'Test Results from ' + dateOfTest.toUTCString();
  resultsContainer.appendChild(resultsHeader);
  
  var resultsList = document.createElement('ul');
  resultsContainer.appendChild(resultsList);
  
  for(var i = 0, len = resultsArray.length; i < len; i++) {
    var listItem = document.createElement('li');
    listItem.innerHTML = resultsArray[i];
    resultsList.appendChild(listItem);
  }
  
  return resultsContainer;
};


// ResultSet Interface.

var ResultSet = new Interface('ResultSet', ['getDate', 'getResults']);

// ResultFormatter class, after adding Interface checking.

var ResultFormatter = function(resultsObject) {
  Interface.ensureImplements(resultsObject, ResultSet);
  this.resultsObject = resultsObject;
};