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JavaScript接口實(shí)現(xiàn)代碼 （Interfaces In JavaScript）

 更新時(shí)間：2010年06月11日 00:30:21   作者：  
接口是面向?qū)ο缶幊汤锏闹匾匦?，遺憾的是JavaScript并沒(méi)有提供對(duì)接口的支持！怎么實(shí)現(xiàn)接口呢？
在實(shí)際中，我們可以在注釋中定義好接口，在實(shí)際的代碼中予以實(shí)現(xiàn)
比如：
復(fù)制代碼 代碼如下:
/*
interface Composite {
function add(child);
function remove(child);
function getChild(index);
}
interface FormItem {
function save();
}
*/
var CompositeForm = function(id, method, action) { // implements Composite, FormItem
...
};
// Implement the Composite interface.
CompositeForm.prototype.add = function(child) {
...
};
CompositeForm.prototype.remove = function(child) {
...
};
CompositeForm.prototype.getChild = function(index) {
...
};
// Implement the FormItem interface.
CompositeForm.prototype.save = function() {
...
};

實(shí)現(xiàn)接口的程序員是否將這些接口都實(shí)現(xiàn)了呢？我們沒(méi)辦法保證！因?yàn)檫@里沒(méi)有任何辦法去檢查是否都實(shí)現(xiàn)了
我們需要一個(gè)檢查是否實(shí)現(xiàn)了接口的機(jī)制，可以這樣：
復(fù)制代碼 代碼如下:
/*
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.");
}
...
}
// The implements function, which checks to see if an object declares that it
// implements the required interfaces.
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.
}

這種方法讓程序員在寫(xiě)的時(shí)候注明實(shí)現(xiàn)了哪些接口： this.implementsInterfaces = ['Composite', 'FormItem']; 在調(diào)用的時(shí)候使用implements方法來(lái)判斷是否實(shí)現(xiàn)了，理論上可行，很有可能寫(xiě)上了實(shí)現(xiàn)了'Composite'接口，但是代碼里卻并沒(méi)有add方法！因此，我們需要檢驗(yàn)實(shí)現(xiàn)接口的類是否包含了接口里的方法！所以，接口必須從注釋中解放出來(lái)：
復(fù)制代碼 代碼如下:
// Interfaces.
var Composite = new Interface('Composite', ['add', 'remove', 'getChild']);
var FormItem = new Interface('FormItem', ['save']);
// CompositeForm class
var CompositeForm = function(id, method, action) { // implements Composite, FormItem
...
};
...
function addForm(formInstance) {
Interface.ensureImplements(formInstance, Composite, FormItem);
// This function will throw an error if a required method is not implemented,
// halting execution of the function.
// All code beneath this line will be executed only if the checks pass.
...
}

定義接口Composite，F(xiàn)ormItem，并且CompositeForm實(shí)現(xiàn)這兩個(gè)接口，在使用的時(shí)候，用Interface.ensureImplements來(lái)檢驗(yàn)formInstance是否實(shí)現(xiàn)了這兩個(gè)接口中的所有方法。
來(lái)看看Interface的定義：兩個(gè)參數(shù)，第一個(gè)參數(shù)是接口名稱，第二個(gè)參數(shù)是接口包含的方法數(shù)組
復(fù)制代碼 代碼如下:
// Constructor.
var Interface = function(name, methods) {
if(arguments.length != 2) {
throw new Error("Interface constructor called with " + arguments.length +
"arguments, but expected exactly 2.");
}
this.name = name;
this.methods = [];
for(var i = 0, len = methods.length; i < len; i++) {
if(typeof methods[i] !== 'string') {
throw new Error("Interface constructor expects method names to be "
+ "passed in as a string.");
}
this.methods.push(methods[i]);
}
};

為Interface 添加建議接口是否實(shí)現(xiàn)的靜態(tài)方法
復(fù)制代碼 代碼如下:
// Constructor.
Interface.ensureImplements = function(object) {
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++) {
var interface = arguments[i];
if(interface.constructor !== Interface) {
throw new Error("Function Interface.ensureImplements expects arguments"
+ "two and above to be instances of Interface.");
}
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.");
}
}
}
};

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