javascript设计模式--接口
最近在看javascript设计模式的书籍《pro javascript design pattrens》,觉得很不错,可以提高自己对js oo的理解,也可能帮助自己更好的理解别人写的js library,提高自己js的水平。
这本书中第一个重要的内容就是接口。
大家对接口应该都不陌生,简单的说接口就是一个契约或者规范。在强类型的面相对象语言中,接口可以很容易的实现。但是在javascript中并没有原生的创建或者实现接口的方式,或者判定一个类型是否实现了某个接口,我们只能利用js的灵活性的特点,模拟接口。
在javascript中实现接口有三种方式:注释描述、属性验证、鸭子模型。
note:因为我看的是英文书,翻译水平有限,不知道有些词汇如何翻译,大家只能领会精神了。
1. 注释描述 (Describing Interfaces with Comments)
例子:
/*
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() {
...
};
模拟其他面向对象语言,使用interface 和 implements关键字,但是需要将他们注释起来,这样就不会有语法错误。
这样做的目的,只是为了告诉其他编程人员,这些类需要实现什么方法,需要在编程的时候加以注意。但是没有提供一种验证方式,这些类是否正确实现了这些接口中的方法,这种方式就是一种文档化的作法。
2. 属性验证(Emulating Interfaces with Attribute Checking)
例子:
/*
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.
}
这种方式比第一种方式有所改进,接口的定义仍然以注释的方式实现,但是添加了验证方法,判断一个类型是否实现了某个接口。
3.鸭子类型(Emulating Interfaces with Duck Typing)
// Interfaces.
var Composite = new Interface('Composite', ['add', 'remove', 'getChild']);
var FormItem = new Interface('FormItem', ['save']);
// CompositeForm class
var CompositeForm = function(id, method, action) {
...
};
...
function addForm(formInstance) {
ensureImplements(formInstance, Composite, FormItem);
// This function will throw an error if a required method is not implemented.
...
}
// 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]);
}
};
// Static class method.
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
&
补充:web前端 , JavaScript ,