每天一篇javascript学习小结（面向对象编程）

内容摘要
1、面向对象的工厂方法




function createPerson(name, age, job){
var o = new Object();
o.name = name;
o.age = age;
o.job = job;
o.sayName = func
文章正文

1、面向对象的工厂方法

 function createPerson(name, age, job){
   var o = new Object();
   o.name = name;
   o.age = age;
   o.job = job;
   o.sayName = function(){
    alert(this.name);
   }; 
   return o;
  }
  
  var person1 = createPerson("Nicholas", 29, "Software Engineer");
  var person2 = createPerson("Greg", 27, "Doctor");
  
  person1.sayName(); //"Nicholas"
  person2.sayName(); //"Greg"

工厂模型的方法的缺点是会产生大量重复代码！

2、构造函数模式创建对象

 function Person(name, age, job){
   this.name = name;
   this.age = age;
   this.job = job;
   this.sayName = function(){
    alert(this.name);
   }; 
  }
  
  var person1 = new Person("Nicholas", 29, "Software Engineer");
  var person2 = new Person("Greg", 27, "Doctor");
  
  person1.sayName(); //"Nicholas"
  person2.sayName(); //"Greg"
  
  alert(person1 instanceof Object); //true
  alert(person1 instanceof Person); //true
  alert(person2 instanceof Object); //true
  alert(person2 instanceof Person); //true
  
  alert(person1.constructor == Person); //true
  alert(person2.constructor == Person); //true
  
  alert(person1.sayName == person2.sayName); //false

 使用new关键字创建对象会经历以下四个过程

  • 1、创建一个新对象
  • 2、将构造函数的作用域赋给一个新对象（因此this就指向了这个新对象）
  • 3、执行构造函数的方法（为这个新对象赋值）
  • 4、返回新对象

3、将构造函数当函数用

 function Person(name, age, job){
   this.name = name;
   this.age = age;
   this.job = job;
   this.sayName = function(){
    alert(this.name);
   };
  }
  
  var person = new Person("Nicholas", 29, "Software Engineer");
  person.sayName(); //"Nicholas"
  
  Person("Greg", 27, "Doctor"); //adds to window
  window.sayName(); //"Greg"
  
  var o = new Object();
  Person.call(o, "Kristen", 25, "Nurse");
  o.sayName(); //"Kristen"

构造函数当做函数使用就和普通的函数没有任何不同，它属于window对象下面添加的方法而已。由于构造函数创建的对象实际上是创建一个新对象，因此在本质上两者还是不一样的，还是分离的，他们的方法还是不一样的！

4、将共有的方法方法全局解决不一致的问题

 function Person(name, age, job){
   this.name = name;
   this.age = age;
   this.job = job;
   this.sayName = sayName;
  }
  
  function sayName(){
   alert(this.name);
  }
  
  var person1 = new Person("Nicholas", 29, "Software Engineer");
  var person2 = new Person("Greg", 27, "Doctor");
  
  person1.sayName(); //"Nicholas"
  person2.sayName(); //"Greg"
  
  alert(person1 instanceof Object); //true
  alert(person1 instanceof Person); //true
  alert(person2 instanceof Object); //true
  alert(person2 instanceof Person); //true
  
  alert(person1.constructor == Person); //true
  alert(person2.constructor == Person); //true
  
  alert(person1.sayName == person2.sayName); //true

虽然上面的方法解决了一致的问题，但是定义的全局的方法本身属于window，那么局部和全局就没有分开！所以这个方法使用的并不多见！也不建议使用。

5、原型模式

我们创建的任何的一个函数都有一个原型对象，这个属性是一个指针，它指向一个对象，而这个对象的作用是可以有特定的类型的所有的实例共享的方法！

 function Person(){
  }
  
  Person.prototype.name = "Nicholas";
  Person.prototype.age = 29;
  Person.prototype.job = "Software Engineer";
  Person.prototype.sayName = function(){
   alert(this.name);
  };
  
  var person1 = new Person();
  person1.sayName(); //"Nicholas"
  
  var person2 = new Person();
  person2.sayName(); //"Nicholas"
  
  alert(person1.sayName == person2.sayName); //true
  
  alert(Person.prototype.isPrototypeOf(person1)); //true
  alert(Person.prototype.isPrototypeOf(person2)); //true
  
  //only works if Object.getPrototypeOf() is available
  if (Object.getPrototypeOf){
   alert(Object.getPrototypeOf(person1) == Person.prototype); //true
   alert(Object.getPrototypeOf(person1).name); //"Nicholas"
  }

理解原型

无论什么时候只要是创建了一个函数，就会创建一个原型属性，这个属性指向函数的原型对象。在默认的情况下，原型对象都会包含一个constructor（构造函数属性），这个属性包含一个指向prototype属性所在函数的指针！

属性读取的顺序

每当代码读取某个对象的属性时候，都会执行一次搜索，目标是具有给定名字的属性，搜索从对象的实例本身开始查找，如有则返回，没有则继续搜索该对象的原型链，直至搜索到原型链的最外层！

 function Person(){
  }
  
  Person.prototype.name = "Nicholas";
  Person.prototype.age = 29;
  Person.prototype.job = "Software Engineer";
  Person.prototype.sayName = function(){
   alert(this.name);
  };
  
  var person1 = new Person();
  var person2 = new Person();
  
  person1.name = "Greg";
  alert(person1.name); //"Greg" 来自实例
  alert(person2.name); //"Nicholas" 来自原型

如果删除了这个元素的实例属性

function Person(){
  }
  
  Person.prototype.name = "Nicholas";
  Person.prototype.age = 29;
  Person.prototype.job = "Software Engineer";
  Person.prototype.sayName = function(){
   alert(this.name);
  };
  
  var person1 = new Person();
  var person2 = new Person();
  
  person1.name = "Greg";
  alert(person1.name); //"Greg" ?from instance
  alert(person2.name); //"Nicholas" ?from prototype
  
  delete person1.name;
  alert(person1.name); //"Nicholas" - from the prototype

6、hasOwnProperty方法

这个方法可以检测一个属性是否存在于实例中，还是存在于原型中！hasOwnProperty是从Object继承来的，只要给定属性存在于对象实例中，才会返回true.

 function Person(){
    }
    
    Person.prototype.name = "Nicholas";
    Person.prototype.age = 29;
    Person.prototype.job = "Software Engineer";
    Person.prototype.sayName = function(){
      alert(this.name);
    };
    
    var person1 = new Person();
    var person2 = new Person();
    
    alert(person1.hasOwnProperty("name")); //false
    alert("name" in person1); //true
    
    person1.name = "Greg";
    alert(person1.name);  //"Greg" ?from instance
    alert(person1.hasOwnProperty("name")); //true
    alert("name" in person1); //true
    
    alert(person2.name);  //"Nicholas" ?from prototype
    alert(person2.hasOwnProperty("name")); //false
    alert("name" in person2); //true
    
    delete person1.name;
    alert(person1.name);  //"Nicholas" - from the prototype
    alert(person1.hasOwnProperty("name")); //false
    alert("name" in person1); //true

7、Object.keys() 可枚举属性方法

这个方法接收一个对象作为参数，返回一个包含所有可枚举属性的字符串数组

 function Person(){
    }
    
    Person.prototype.name = "Nicholas";
    Person.prototype.age = 29;
    Person.prototype.job = "Software Engineer";
    Person.prototype.sayName = function(){
      alert(this.name);
    };
    
    var keys = Object.keys(Person.prototype);
    alert(keys);  //"name,age,job,sayName"
如果想得到所有实例的属性，无论它是否可以枚举都可以使用这个方法来获取
 function Person(){
    }
    
    Person.prototype.name = "Nicholas";
    Person.prototype.age = 29;
    Person.prototype.job = "Software Engineer";
    Person.prototype.sayName = function(){
      alert(this.name);
    };
    
    var keys = Object.getOwnPropertyNames(Person.prototype);
    alert(keys);  //"constructor,name,age,job,sayName"

此方法高版本浏览器才支持

8、简单的原型写法

 function Person(){
    }
    
    Person.prototype = {
      name : "Nicholas",
      age : 29,
      job: "Software Engineer",
      sayName : function () {
        alert(this.name);
      }
    };

    var friend = new Person();
    
    alert(friend instanceof Object); //true
    alert(friend instanceof Person); //true
    alert(friend.constructor == Person); //false
    alert(friend.constructor == Object); //true

重写了原型就等于将默认的原型方法覆盖，那么同样的构造方法也会被重写，重写的构造方法指向了Object对象！而不是原来的对象Person

如果还是想指向之前的构造方法，可以显示的指定

 function Person(){
    }
    
    Person.prototype = {
      constructor : Person,
      name : "Nicholas",
      age : 29,
      job: "Software Engineer",
      sayName : function () {
        alert(this.name);
      }
    };

    var friend = new Person();
    
    alert(friend instanceof Object); //true
    alert(friend instanceof Person); //true
    alert(friend.constructor == Person); //true
    alert(friend.constructor == Object); //false

9、原型方法的动态添加

function Person(){
    }
    
    Person.prototype = {
      constructor: Person,
      name : "Nicholas",
      age : 29,
      job : "Software Engineer",
      sayName : function () {
        alert(this.name);
      }
    };
    
    var friend = new Person();
    
    Person.prototype.sayHi = function(){
      alert("hi");
    };
    
    friend.sayHi();  //"hi" ?works!

10、原生对象的原型方法

alert(typeof Array.prototype.sort);     //"function"
    alert(typeof String.prototype.substring);  //"function"

    String.prototype.startsWith = function (text) {//修改原生对象的原型方法
      return this.indexOf(text) == 0;
    };
    
    var msg = "Hello world!";
    alert(msg.startsWith("Hello"));  //true

11、组合使用构造函数和原型模式创建对象

//构造函数模式
function Person(name, age, job){
      this.name = name;
      this.age = age;
      this.job = job;
      this.friends = ["Shelby", "Court"];
    }
    //原型模式
    Person.prototype = {
      constructor: Person,
      sayName : function () {
        alert(this.name);
      }
    };
    
    var person1 = new Person("Nicholas", 29, "Software Engineer");
    var person2 = new Person("Greg", 27, "Doctor");
    
    person1.friends.push("Van");
    
    alert(person1.friends);  //"Shelby,Court,Van"
    alert(person2.friends);  //"Shelby,Court"
    alert(person1.friends === person2.friends); //false
    alert(person1.sayName === person2.sayName); //true

12、动态原型模式

function Person(name, age, job){
    
      //properties
      this.name = name;
      this.age = age;
      this.job = job;
      
      //methods
      if (typeof this.sayName != "function"){
      
        Person.prototype.sayName = function(){
          alert(this.name);
        };
        
      }
    }

    var friend = new Person("Nicholas", 29, "Software Engineer");
    friend.sayName();

13、寄生构造函数模式

 function Person(name, age, job){
var o = new Object();//依赖全局对象初始化一个对象，然后再返回这个对象
o.name = name;
o.age = age;
o.job = job;
o.sayName = function(){
alert(this.name);
}; 
return o;
}

var friend = new Person("Nicholas", 29, "Software Engineer");
friend.sayName(); //"Nicholas"

function SpecialArray(){ 

//create the array
var values = new Array();

//add the values
values.push.apply(values, arguments);

//assign the method
values.toPipedString = function(){
return this.join("|");
};

//return it
return values; 
}

var colors = new SpecialArray("red", "blue", "green");
alert(colors.toPipedString()); //"red|blue|green"

alert(colors instanceof SpecialArray);

上诉方法有一点说明下，由于它是依赖外层对象来创建一个新对象，因此不能依赖 instanceof方法来确定属性和方法的来源！它实际上和构造函数的没有关系！

14、稳妥构造函数模式

 function Person(name, age, job){
      var o = new Object();
      o.sayName = function(){
        alert(name);
      };  
      return o;
    }
    
    var friend = Person("Nicholas", 29, "Software Engineer");
    friend.sayName(); //"Nicholas"

此方法不依赖任何new this 关键符！如果要访问对象的方法和属性，只能通过对象已经定义好的方法来获取！

15、继承
javascript实现继承是通过原型链来实现的

function SuperType(){
      this.property = true;//定义一个属性
    }
    
    SuperType.prototype.getSuperValue = function(){//定义的原型方法
      return this.property;
    };
    
    function SubType(){
      this.subproperty = false;
    }
    
    //inherit from SuperType
    SubType.prototype = new SuperType();
    
    SubType.prototype.getSubValue = function (){
      return this.subproperty;
    };
    
    var instance = new SubType();
    alert(instance.getSuperValue());  //true
    
    alert(instance instanceof Object);   //true
    alert(instance instanceof SuperType);  //true
    alert(instance instanceof SubType);   //true

    alert(Object.prototype.isPrototypeOf(instance));  //true
    alert(SuperType.prototype.isPrototypeOf(instance)); //true
    alert(SubType.prototype.isPrototypeOf(instance));  //true
SubType继承SuperType的方法和属性，因此当instance可以直接调用SuperType的方法！
 function SuperType(){
      this.property = true;
    }
    
    SuperType.prototype.getSuperValue = function(){
      return this.property;
    };
    
    function SubType(){
      this.subproperty = false;
    }
    
    //inherit from SuperType
    SubType.prototype = new SuperType();
    
    //new method
    SubType.prototype.getSubValue = function (){
      return this.subproperty;
    };
    
    //override existing method
    SubType.prototype.getSuperValue = function (){
      return false;
    };
    
    var instance = new SubType();
    alert(instance.getSuperValue());  //false

上面的例子说明，重写的原型会覆盖之前继承的原型，最后返回的往往不是预期的效果

 function SuperType(){
      this.property = true;
    }
    
    SuperType.prototype.getSuperValue = function(){
      return this.property;
    };
    
    function SubType(){
      this.subproperty = false;
    }
    
    //inherit from SuperType
    SubType.prototype = new SuperType();
    
    //使用字面量添加的方法导致上面的方法失效了
    SubType.prototype = {
      getSubValue : function (){
        return this.subproperty;
      },
    
      someOtherMethod : function (){
        return false;
      }
    }; 
    
    var instance = new SubType();
    console.log(instance);
    alert(instance.getSuperValue());  //error!

下面的例子也说明重写原型带来的风险

 function SuperType(){
      this.colors = ["red", "blue", "green"];
    }

    function SubType(){      
    }
    
    //inherit from SuperType
    SubType.prototype = new SuperType();

    var instance1 = new SubType();
    instance1.colors.push("black");
    alert(instance1.colors);  //"red,blue,green,black"
    
    var instance2 = new SubType();
    alert(instance2.colors);  //"red,blue,green,black"

原型共享导致两个不同的对象调用的同一个数据
16、借用构造函数来实现继承

 function SuperType(){
      this.colors = ["red", "blue", "green"];
    }

    function SubType(){ 
      //inherit from SuperType
      SuperType.call(this);
    }

    var instance1 = new SubType();
    instance1.colors.push("black");
    alert(instance1.colors);  //"red,blue,green,black"
    
    var instance2 = new SubType();
    alert(instance2.colors);  //"red,blue,green"

传递参数

 function SuperType(name){
      this.name = name;
    }

    function SubType(){ 
      //inherit from SuperType passing in an argument
      SuperType.call(this, "Nicholas");
      
      //instance property
      this.age = 29;
    }

    var instance = new SubType();
    alert(instance.name);  //"Nicholas";
    alert(instance.age);   //29

17、组合继承方式

function SuperType(name){
      this.name = name;
      this.colors = ["red", "blue", "green"];
    }
    
    SuperType.prototype.sayName = function(){
      alert(this.name);
    };

    function SubType(name, age){ 
      SuperType.call(this, name);
      
      this.age = age;
    }

18、原型继承

 function object(o){
      function F(){}
      F.prototype = o;
      return new F();
    }
    
    var person = {
      name: "Nicholas",
      friends: ["Shelby", "Court", "Van"]
    };
    
    var anotherPerson = object(person);
    anotherPerson.name = "Greg";
    anotherPerson.friends.push("Rob");

19、寄生组合式继承

 function object(o){
      function F(){}
      F.prototype = o;
      return new F();
    }
  
    function inheritPrototype(subType, superType){
      var prototype = object(superType.prototype);  //create object
      prototype.constructor = subType;        //augment object
      subType.prototype = prototype;         //assign object
    }
                
    function SuperType(name){
      this.name = name;
      this.colors = ["red", "blue", "green"];
    }
    
    SuperType.prototype.sayName = function(){
      alert(this.name);
    };

    function SubType(name, age){ 
      SuperType.call(this, name);
      
      this.age = age;
    }

    inheritPrototype(SubType, SuperType);
    
    SubType.prototype.sayAge = function(){
      alert(this.age);
    };
    
    var instance1 = new SubType("Nicholas", 29);
    instance1.colors.push("black");
    alert(instance1.colors); //"red,blue,green,black"
    instance1.sayName();   //"Nicholas";
    instance1.sayAge();    //29
    
    
    var instance2 = new SubType("Greg", 27);
    alert(instance2.colors); //"red,blue,green"
    instance2.sayName();   //"Greg";
    instance2.sayAge();    //27

以上就是今天的javascript学习小结，之后每天还会继续更新，希望大家继续关注。
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