12.02 - In what ways can a decorator modify its component.js

// 在方法之后添加行为
HeadlightDecorator.prototype.getPrice = function() {
  return this.bicycle.getPrice() + 15.00;
};
// 创建一辆带有两个前灯和一个尾灯的自行车
var myBicycle = new AcmeComfortCruiser(); // Instantiate the bicycle.
alert(myBicycle.getPrice()); // Returns 399.00

myBicycle = new HeadlightDecorator(myBicycle); // Decorate the bicycle object
                                               // with the first headlight.
myBicycle = new HeadlightDecorator(myBicycle); // Decorate the bicycle object
                                               // with the second headlight.
myBicycle = new TaillightDecorator(myBicycle); // Decorate the bicycle object
                                               // with a taillight.
alert(myBicycle.getPrice()); // Now returns 438.00


/* FrameColorDecorator class. */
// 在方法之前添加行为
var FrameColorDecorator = function(bicycle, frameColor) { // implements Bicycle
  this.superclass.constructor(bicycle); // Call the superclass's constructor.
  this.frameColor = frameColor;
}
extend(FrameColorDecorator, BicycleDecorator); // Extend the superclass.
FrameColorDecorator.prototype.assemble = function() {
  return 'Paint the frame ' + this.frameColor + ' and allow it to dry. ' + 
      this.bicycle.assemble();
};
// 在方法后添加行为
FrameColorDecorator.prototype.getPrice = function() {
  return this.bicycle.getPrice() + 30.00;
}; 

var myBicycle = new AcmeComfortCruiser(); // Instantiate the bicycle.
myBicycle = new FrameColorDecorator(myBicycle, 'red'); // Decorate the bicycle
                                               // object with the frame color.
myBicycle = new HeadlightDecorator(myBicycle); // Decorate the bicycle object
                                               // with the first headlight.
myBicycle = new HeadlightDecorator(myBicycle); // Decorate the bicycle object
                                               // with the second headlight.
myBicycle = new TaillightDecorator(myBicycle); // Decorate the bicycle object
                                               // with a taillight.
alert(myBicycle.assemble()); 
/* Returns:
    "Paint the frame red and allow it to dry. (Full instructions for assembling
    the bike itself go here) Attach headlight to handlebars. Attach headlight 
    to handlebars. Attach taillight to the seat post."
*/




/* LifetimeWarrantyDecorator class. */
// 替换方法
var LifetimeWarrantyDecorator = function(bicycle) { // implements Bicycle
  this.superclass.constructor(bicycle); // Call the superclass's constructor.
}
extend(LifetimeWarrantyDecorator, BicycleDecorator); // Extend the superclass.
LifetimeWarrantyDecorator.prototype.repair = function() {
  return 'This bicycle is covered by a lifetime warranty. Please take it to ' +
      'an authorized Acme Repair Center.';
};
LifetimeWarrantyDecorator.prototype.getPrice = function() {
  return this.bicycle.getPrice() + 199.00;
};

/* TimedWarrantyDecorator class. */
// 下面这个例子创建的装饰着用于实现规定了保修期的保修，在满足条件时替换方法，否则就使用组件方法
var TimedWarrantyDecorator = function(bicycle, coverageLengthInYears) { 
    // implements Bicycle
  this.superclass.constructor(bicycle); // Call the superclass's constructor.
  this.coverageLength = coverageLengthInYears;
  this.expDate = new Date();
  var coverageLengthInMs = this.coverageLength * 365 * 24 * 60 * 60 * 1000;
  expDate.setTime(expDate.getTime() + coverageLengthInMs);
}
extend(TimedWarrantyDecorator, BicycleDecorator); // Extend the superclass.
TimedWarrantyDecorator.prototype.repair = function() {
  var repairInstructions;
  var currentDate = new Date();
  if(currentDate < expDate) {
    repairInstructions = 'This bicycle is currently covered by a warranty. ' +
        'Please take it to an authorized Acme Repair Center.';
  }
  else {
    repairInstructions = this.bicycle.repair();
  }
  return repairInstructions;
};
TimedWarrantyDecorator.prototype.getPrice = function() {
  return this.bicycle.getPrice() + (40.00 * this.coverageLength);
};


// 添加新方法
/* BellDecorator class. */
/**
 * 在装饰着中添加新方法又是也是为类增加功能的一种强有力的手段。
 * 我们可以用这种装饰者为自行车对象增添一个按铃方法。
 * 这是一个新功能，没有装饰者自行车就不可能执行这个任务
 */
var BellDecorator = function(bicycle) { // implements Bicycle
  this.superclass.constructor(bicycle); // Call the superclass's constrcutor.
}
extend(BellDecorator, BicycleDecorator); // Extend the superclass.
BellDecorator.prototype.assemble = function() {
  return this.bicycle.assemble() + ' Attach bell to handlebars.';
};
BellDecorator.prototype.getPrice = function() {
  return this.bicycle.getPrice() + 6.00;
};
// 新增的方法
BellDecorator.prototype.ringBell = function() {
  return 'Bell rung.';
};

var myBicycle = new AcmeComfortCruiser(); // Instantiate the bicycle.
myBicycle = new BellDecorator(myBicycle); // Decorate the bicycle object 
                                          // with a bell.
alert(myBicycle.ringBell()); // Returns 'Bell rung.'

var myBicycle = new AcmeComfortCruiser(); // Instantiate the bicycle.
// BellDecorator必须放在最后应用，否则这个新方法将无法访问。
myBicycle = new BellDecorator(myBicycle); // Decorate the bicycle object 
                                          // with a bell.
myBicycle = new HeadlightDecorator(myBicycle); // Decorate the bicycle object
                                               // with a headlight.                                          
alert(myBicycle.ringBell()); // Method not found.



/* The BicycleDecorator abstract decorator class, improved. */
/**
 *  解决上面所说的BellDeorator必须放在最后应用，否则这个新方法无法访问的方法：
 *  在BycleDecorator的构造函数中添加一些代码，它们对组件对象进行检查，
 *  并为其拥有的每一个方法创建一个通道方法。这样一来，如果在BellDecorator外再裹上另一个装饰者的话
 *  内层装饰着定义的新方法仍然可以访问。
 */
var BicycleDecorator = function(bicycle) { // implements Bicycle
  this.bicycle = bicycle;
  this.interface = Bicycle;
  
  // Loop through all of the attributes of this.bicycle and create pass-through
  // methods for any methods that aren't currently implemented.
  outerloop: for(var key in this.bicycle) {
    // Ensure that the property is a function.
    if(typeof this.bicycle[key] !== 'function') {
      continue outerloop;
    }
    
    // Ensure that the method isn't in the interface.
    for(var i = 0, len = this.interface.methods.length; i < len; i++) {
      if(key === this.interface.methods[i]) {
        continue outerloop;
      }
    }
    
    // Add the new method.
    var that = this;
    (function(methodName) {
      that[methodName] = function() {
        return that.bicycle[methodName]();
      };
    })(key); 
  }
}
BicycleDecorator.prototype = {
  assemble: function() {
    return this.bicycle.assemble();
  },
  wash: function() {
    return this.bicycle.wash();
  },
  ride: function() {
    return this.bicycle.ride();
  },
  repair: function() {
    return this.bicycle.repair();
  },
  getPrice: function() {
    return this.bicycle.getPrice();
  }
};