JavaScript装饰者模式详解：动态扩展对象功能的三种实现方式

//需要装饰的类（函数）
function Macbook() {
 this.cost = function () {
  return 1000;
 };
} 
//计算商品的包装费
function PackagingFee(macbook) {
 this.cost = function () {
  return macbook.cost() + 75;
 };
}
//计算商品的运费
function Freight(macbook) {
 this.cost = function () {
  return macbook.cost() + 300;
 };
} 
//计算商品的保险费用
function Insurance(macbook) {
 this.cost = function () {
  return macbook.cost() + 250;
 };
}
// 用法
var myMacbook = new Insurance(new Freight(new PackagingFee(new Macbook())));
console.log(myMacbook.cost());//1625

// 用法
var myMacbook = new Insurance(new Freight(new PackagingFee(new Macbook())));
console.log(myMacbook.cost());//1625 
//上面的代码等价于下面拆分后的代码，或许拆分后代码你更能看出前后的逻辑性
var macbook = new Macbook();
var package = new PackagingFee(macbook);
var freight = new Freight(package);
var myMacbook = new Insurance(freight);
//当然，如果你不想声明这么多变量（macbook、package、freight），只用一个变量也是可以的
var macbook = new Macbook();
macbook = new PackagingFee(macbook);
macbook = new Freight(macbook);
var myMacbook = new Insurance(macbook);

function ConcreteClass() {
 this.performTask = function () {
  this.preTask();
  console.log('doing something');
  this.postTask();
 };
}
function AbstractDecorator(decorated) {
 this.performTask = function () {
  decorated.performTask();
 };
}
function ConcreteDecoratorClass(decorated) {
 this.base = AbstractDecorator;
 this.base(decorated);// add performTask method
 decorated.preTask = function () {
  console.log('pre-calling..');
 };
 decorated.postTask = function () {
  console.log('post-calling..');
 };
}
var concrete = new ConcreteClass();
var decorator1 = new ConcreteDecoratorClass(concrete);
decorator1.performTask();
//pre-calling..
//doing something
//post-calling..

var concrete = new ConcreteClass(); //声明一个变量concrete指向new出来的ConcreteClass对象
var decorator1 = new ConcreteDecoratorClass(concrete); //声明一个变量decorator1指向new出来的ConcreteDecoratorClass对象，并传入变量concrete作为形参

this.base = AbstractDecorator; //定义一个当前对象（decorator1）的base属性，并指向函数AbstractDecorator
this.base(decorated); //调用base属性指向的函数，也就是调用AbstractDecorator函数，同时传入形参decorated，形参decorated指向new出来的ConcreteClass对象

var tree = {};
tree.decorate = function () {
 console.log('Make sure the tree won\'t fall');
}; 
tree.getDecorator = function (deco) {
 tree[deco].prototype = this;
 return new tree[deco];
}; 
tree.RedApples = function () {
 this.decorate = function () {
  this.RedApples.prototype.decorate(); // 第7步：先执行原型（这时候是Angel了）的decorate方法
  console.log('Add some red apples'); // 第8步 再输出 red
  // 将这2步作为RedApples的decorate方法
 }
};
tree.BlueApples = function () {
 this.decorate = function () {
  this.BlueApples.prototype.decorate(); // 第1步：先执行原型的decorate方法，也就是tree.decorate()
  console.log('Put on some blue apples'); // 第2步 再输出blue
  // 将这2步作为BlueApples的decorate方法
 }
}; 
tree.Angel = function () {
 this.decorate = function () {
  this.Angel.prototype.decorate(); // 第4步：先执行原型（这时候是BlueApples了）的decorate方法
  console.log('An angel on the top'); // 第5步 再输出angel
  // 将这2步作为Angel的decorate方法
 }
};
tree = tree.getDecorator('BlueApples'); // 第3步：将BlueApples对象赋给tree，这时候父原型里的getDecorator依然可用
tree = tree.getDecorator('Angel'); // 第6步：将Angel对象赋给tree，这时候父原型的父原型里的getDecorator依然可用
tree = tree.getDecorator('RedApples'); // 第9步：将RedApples对象赋给tree
tree.decorate(); // 第10步：执行RedApples对象的decorate方法
//Make sure the tree won't fall
//Add blue apples
//An angel on the top
//Put on some red apples

//tree.getDecorator('BlueApples')返回new出来的tree.BlueApples的实例对象，并将该对象赋值给空的tree对象
tree = tree.getDecorator('BlueApples'); //new出来的tree.BlueApples的实例对象的原型指向 --> 空对象tree 
//tree.getDecorator('Angel')返回new出来的tree.Angel的实例对象（这行代码中的第二个tree已经是上面一行代码运行结果后的tree.BlueApples的实例对象）
tree = tree.getDecorator('Angel'); //new出来的tree.Angel的实例对象的原型指向 --> tree.BlueApples的实例对象
//tree.getDecorator('RedApples')返回new出来的tree.RedApples的实例对象（这行代码中的第二个tree已经是上面一行代码运行结果后的tree.Angel的实例对象）
tree = tree.getDecorator('RedApples'); //new出来的tree.RedApples的实例对象的原型指向 --> tree.Angel的实例对象
//调用tree.decorate()，这里的tree已经是new出来的tree.RedApples的实例对象了。
//tree.RedApples的实例对象的decorate属性方法里面的第一行代码是 “this.RedApples.prototype.decorate()”
//结合上面的分析可以得出以下的原型链结构：
//this.RedApples.prototype --> tree.Angel;
//tree.Angel.prototype --> tree.BlueApples;
//tree.BlueApples.prototype --> 空对象tree
tree.decorate();