原生js实现继承

　　在多数语言中继承都很重要。JavaScript是一个基于原型的语言，这意味着对象可以直接从其他对象继承。以下列出几种常见的js继承方式。

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1. 原型链继承

   function Father(){ 
    this.status = true; 
   } 
   Father.prototype.getSuper = function(){ 
    return this.status; 
   }; 
   function Son(){ 
    this.substatus = false; 
   } 
   //继承了 SuperType 
   Son.prototype = new Father(); 
   Son.prototype.getSub = function (){ 
    return this.substatus; 
   }; 
   var instance = new Son(); 
   alert(instance.getSuper()); //true

2. 借用构造函数继承

   function Father(){ 
    this.colors = [1,2,3]; 
   } 
   function Son(){ 
    //继承了 Father
    Father.call(this); 
   } 
   var instance1 = new Son(); 
   instance1.colors.push(4); 
   alert(instance1.colors); //"1,2,3,4" 
   var instance2 = new Son(); 
   alert(instance2.colors); //"1,2,3"
3. 组合继承

   function Father(name){ 
     this.name = name; 
   } 
   Father.prototype.sayName = function(){ 
     alert(this.name);
   }; 
   function Son(name, age){ 
     //继承属性
     SuperType.call(this, name); 
     this.age = age; 
   } 
   
   Son.prototype = new Father(); //将子类的原型指向父类
   Son.prototype.constructor = Son; //将子类的constructor指向自己
   Son.prototype.sayAge = function(){ 
     alert(this.age); 
   }; 
   var instance = new Son("lh", 19); 
   instance1.sayName(); //"lh"; 
   instance1.sayAge(); //19 
   

4. 原型式继承

   function object(o){ 
     function F(){} 
     F.prototype = o; 
     return new F(); 
   }
   var person = { 
     name: "lh", 
     loves: ["a", "b", "c"] 
   }; 
   var anotherPerson = object(person); 
   anotherPerson.name = "Greg"; 
   anotherPerson.friends.push("d");  
   alert(person.loves); //"a,b,c,d"

    这里的object方法和Object.create()方法类似。

5. 寄生式继承

   function object(o){ 
     function F(){} 
     F.prototype = o; 
     return new F(); 
   }
   function createAnother(obj){ 
     var clone = object(obj); //通过调用函数创建一个新对象
     clone.say = function(){ //给这个对象添加方法
     alert("hi"); 
     }; 
     return clone; //返回这个对象
   }
   var person = { 
     name: "lh", 
     loves: ["a", "b", "c"] 
   }; 
   var anotherPerson = createAnother(person); 
   anotherPerson.say(); //"hi"

6. 寄生组合式继承

   function inheritPrototype(son, father){ 
     var prototype = Object.create(father.prototype); 
      son.prototype = prototype; 
   　　prototype.constructor = son;
   }
   function Father(name){ 
    this.name = name; 
   } 
   Father.prototype.sayName = function(){ 
    alert(this.name); 
   }; 
   function Son(name, age){ 
    Father.call(this, name); 
    this.age = age; 
   } 
   inheritPrototype(Son, Father); 
   

7. 使用es6实现

   class Father{
     constructor(x, y) {
       this.x = x;
       this.y = y;
     }
   }
   class son extends Father{
     constructor(x, y, age) {
       super(x, y); // 调用父类的constructor(x, y)
       this.age= age;
     }
     toString() {
       return this.color + ' ' + super.toString(); // 调用父类的toString()
     }
   }

　　　　子类继承父类中constructor中必须先调用super()方法才能访问this，否则会报错。