/**
* 接口是一种指定对象应该有哪些方法的技术，他不关心方法如何实现。
* 基于接口编程的好处是：实现相同接口的对象，可以互换，而不影响功能实现。
* 接口还有利于大项目中，多人合作的交流
*/
/**************** 在js中模仿接口 ******************/
//用注释描述接口
//效果最差，不会提供错误信息
//易于实现
/*
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) {
};
Composite.prototype.getChild = function (index) {
};
//implement the formItem interface
CompositeForm.prototype.save = function () {
};
//用属性检查模仿接口
/*
优点：
对类所实现的接口提供了文档说明
如果没有必须的接口会提示错误消息
缺点：
显示声明类所支持的接口，但没有真正检测接口是否存在
*/
/*
interface COMposite {
function add(child);
function remove(child);
function getChild(index);
}
interface FormItem {
function save();
}
*/
var CompositeForm = function (id, method, action) {
//add interface into array
this.implementsInterfaces = ['Composite', 'FormItem'];
//...
};
function addForm(formInstance) {
if (!implements(formInstance, 'Composite', 'formItem')) {
throw new Error('Object does not implement a required interface.');
}
//...
}
//The implement function,which checks to see if an object declares that
//it implements the required interface
function implements(object) {
//looping through all arguments after the first one
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) {
//an interface was not found
return false;
}
}
//all interface were found
return true;
}
//用鸭式辩型模仿接口
//如果对象具有与接口定义的方法同名的所有方法
//那么就可以认为它实现了这个接口
/**
* 三种方法中最有用的一种
* 缺点：
* 类并不声明自己实现了那些接口，降低了代码的可重用性
* 缺乏自我描述
* 不检查方法的参数
*/
//Interface.
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
//...
}
//本书采用的接口实现方法
//结合第一种和第三种方法
//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) {
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
//...
}
/************ Interface类 *************/
//Constructor
var Interface = function (name, method) {
// 检测参数个数
if (arguments.length != 2) {
throw new Error('Interface constructor called with ' + arguments.length + 'arguments,ut expected exactly 2.');
}
this.name = name;
this.methods = [];
//遍历方法
for (var i = 0, len = method.length; i < len; i++) {
//检查数组值是否字符串
//如果不是，抛出错误信息
if (typeof method[i] !== 'string') {
throw new Error('Interface constructor expects method names to be passed in as a string');
}
//将方法名添加到属性数组中
this.methods.push(method[i]);
}
};
//static class method
Interface.ensureImplements = function (object) {
//参数个数必须大于等于2个
if (arguments.length < 2) {
throw new Error('Function Interface.ensureImplements called with ' + arguments.length + 'arguments,but expected at least 2.');
}
//遍历除第一个参数的其他参数
for (var i = 1, len = arguments.length; i < len; i++) {
var interface = arguments[i];
//如果不是Interface的实例，则抛出错误
if (interface.constructor !== Interface) {
throw new Error('Function interface.ensureImplements expectes arguments two and above to be instances of Interface.');
}
//遍历实例中的方法
for (var j = 0, methodsLen = interface.methods.length; j < methodsLen; j++) {
var method = interface.methods[j];
//如果object没有实例中的方法，则抛出错误
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.');
}
}
}
};
//使用
var DynamicMap = new Interface('DybamicMap', ['centerOnPoint', 'zoom', 'draw']);
function displayRoute(mapInstance) {
Interface.ensureImplements(mapInstance, DynamicMap);
mapInstance.centerOnPoint(12, 34);
mapInstance.zoom(5);
mapInstance.draw();
//...
}
var Test = function () {
};
Test.prototype = {
centerOnPoint:function (a, b) {
console.log('centerOnPoint2');
},
zoom:function (num) {
console.log('zoom2');
},
draw:function(){
}
};
var a = new Test();
displayRoute(a);
//实例
// ResultFormatter class,before we implement interface checking
//未使用Interface类检测
var TestResult = function () {
};
TestResult.prototype = {
getDate:function () {
},
getResults:function () {
}
};
var ResultFormatter = function (resultsObject) {
// 是否为TestResult的实例
// 不是就抛出错误
if (!(resultsObject instanceof TestResult)) {
throw new Error('ResultsFormatter: constructor requires an instance of TestResult as an argument.');
}
//将参数公有化
this.resultsObject = resultsObject;
};
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);
}
//返回创建的DOM
return resultsContainer;
};
/*
TestResult类可能被修改，致使其不再拥有getDate()方法
检查仍能通过，但renderResults方法却会失灵
不允许其他类的实例作为参数
*/
//使用Interface类后
//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;
};
ResultFormatter.prototype.renderResults=function(){
//...
};