javascript优化--10模式(设计模式)01

单体模式：保证一个特定类仅有一个实例;即第二次使用同一个类创建新对象时，应该得到与第一个所创建对象完全相同对象；

• 在JS中，可以认为每次在使用对象字面量创建对象的时候，实际上就在创建一个单体；
• 当使用new创建新对象时
  • 使用静态属性中的实例：

    function Universe() {
    	if(typeof Universe.instance === 'object') {
    		return Universe.instance;
    	}
    	this.start_time = 0;
    	this.bang = 'Big';
    	Universe.instance = this;
    	return this;
    }　　

  • 采用闭包包含单个实例：

    function Universe1() {
    	var instance = this;
    	this.start_time = 0;
    	this.bang = 'Big';
    	Universe1 = function() {
    		return instance;
    	}
    }
    

    var Universe;
    (function () {
    	var instance;
    	Universe = function Universe() {
    		if(instance) {
    			return instance;
    		}
    		instance = this;
      //增加功能
    		this.start_time = 0;
    		this.bang = 'Big';
    	}
    })();

工厂模式：

根据字符串指定地类型在运行时创建对象地方法

工厂模式地目的使为了创建对象

• 当创建对象时执行重复操作
• 再编译时不知道具体类型地情况下，为工厂客户提供一个创建对象的接口

function CarMaker() {};

CarMaker.prototype.drive = function() {
  return "Vroom, I have  " + this.doors + " doors";
};
CarMaker.factory = function(type) {
  var constr = type, newcar;
  //如果构造函数不存在，则抛出错误
  if(typeof CarMaker[constr] != "function") {
    throw {
        name: "Error",
        message: constr + " doesn't exist"
    };
  }
  //构造函数是已知存在的；使原型继承父类，但仅继承一次
  if(typeof CarMaker[constr].prototype.drive !== 'function') {
    CarMaker[constr].prototype = new CarMaker();
  }
  //创建一个新的实例
  newcar = new CarMaker[constr]();
  //选择性地调用一些方法，然后返回
  return newcar;
};

CarMaker.Compact = function() {
  this.doors = 4;
};
CarMaker.Convertible = function() {
  this.doors = 2;
}
CarMaker.SUV = function() {
  this.doors = 24;
}

var corolla = CarMaker.factory('Compact');
var solstice = CarMaker.factory('Convertible');
var cherokee = CarMaker.factory('SUV');
corolla.drive()；
solstice.drive()；
cherokee.drive()；

内置对象工厂：对于自然工厂的例子，可以考虑内置的Object()构造函数；它也根据输入类型而创建不同的对象；

迭代器模式：

提供一个API来遍历或操纵复杂地自定义数据结构

迭代访问一个包含某些数据集合的对象的模式；

var agg = (function() {
  var index = 0, data = [1,2,3,4,5], length = data.length;
  return {
    next: function() {
      var element;
      if(!this.hasNext()) {
        return null;
      }
      element = data[index];
      index = index + 2;
      return element;
    },
    hasNext: function() {
      return index < length;
    },
    //重置指针到初始化位置
    rewind: function() {
      index = 0;
    },
    //返回当前元素
    current: function() {
      return data[index];
    }
  }
}());
//测试
while(agg.hasNext()) {
  console.log(agg.next());
}
agg.rewind();
console.log(agg.current());

装饰者模式

可以再运行时动态添加附加功能到对象中；比较方便的特征时其预期行为可制定和可配置；

function Sale(price) {
  this.price = price || 100;
}
Sale.prototype.getPrice = function() {
  return this.price;
}
Sale.decorators = {};
//增加联邦税
Sale.decorators.fedtax = {
  getPrice: function() {
    var price = this.uber.getPrice();
    price += price * 5/ 100;
    return price;
  }
};
//增加省级税
Sale.decorators.quebec = {
  getPrice: function() {
    var price = this.uber.getPrice();
    price += price * 7.5 /100;
    return price;
  }
};
//转化为美元
Sale.decorators.money = {
  getPrice: function() {
    return "$" + this.uber.getPrice().toFixed(2);
  }
};
//格式化为CDN
Sale.decorators.cdn = {
  getPrice: function() {
    return "CDN$ " + this.uber.getPrice().toFixed(2);
  }
};
Sale.prototype.decorate = function(decorator) {
  var F = function() {},
      overrides = this.constructor.decorators[decorator],
      i, newobj;
  F.prototype = this;
  newobj = new F();
  newobj.uber = F.prototype;
  for(i in overrides) {
    if(overrides.hasOwnProperty(i)) {
      newobj[i] = overrides[i];
    }
  }
  return newobj;
}

var sale = new Sale(100);
sale = sale.decorate('fedtax');
sale = sale.decorate('quebec');
sale = sale.decorate('money');
sale.getPrice();
var newsale = new Sale(200);
newsale = newsale.decorate('cdn');
newsale.getPrice();

使用列表实现

function Sale(price) {
  this.price = price;
  this.decorators_list = [];
}
Sale.decorators = {};
Sale.decorators.fedtax = {
  getPrice: function(price) {
    return price + price * 5 / 100;
  }
};
Sale.decorators.quebec = {
  getPrice: function(price) {
    return price + price * 7.5 /100;
  }
};
Sale.decorators.money = {
  getPrice: function(price) {
    return "$" + price.toFixed(2);
  }
};
Sale.prototype.decorate = function(decorator) {
  this.decorators_list.push(decorator)
};
Sale.prototype.getPrice = function() {
  var price = this.price, i, max = this.decorators_list.length, name;
  for(i = 0; i < max; i++) {
    name = this.decorators_list[i];
    price = Sale.decorators[name].getPrice(price);
  }
  return price;
}

var sale = new Sale(100);
sale.decorate('fedtax');
sale.decorate('quebec');
sale.decorate('money');
console.log(sale.getPrice());