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;
};