JS继承重识

JS继承的主要方法是通过原型链让一个引用类型继承另一个引用类型的属性和方法。通常的做法也可以表述为，让一个构造函数的原型对象等于另一个类型都实例。

例如基本形式如下：

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

常用的继承方法有

借用构造函数继承：

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

借助构造函数继承传参：

function SuperType(name){ 
 this.name = name; 
} 
function SubType(){ 
 //继承了 SuperType，同时还传递了参数
 SuperType.call(this, "Nicholas"); 
 //实例属性
 this.age = 29; 
} 
var instance = new SubType(); 
alert(instance.name); //"Nicholas"; 
alert(instance.age); //29

---

组合继承（最常用）

 

使用原型链实现对原型属性和方法的继承，而通过借用构造函数来实现对实例属性的继承。这样，既通过在原型上定义方法实现了函数 复用，又能够保证每个实例都有它自己的属性。例如：

function SuperType(name){ 
 this.name = name; 
 this.colors = ["red", "blue", "green"]; 
} 
SuperType.prototype.sayName = function(){ 
 alert(this.name);
}; 
function SubType(name, age){ 
 //继承属性
 SuperType.call(this, name); 
 this.age = age; 
} 
//继承方法
SubType.prototype = new SuperType(); 
SubType.prototype.constructor = SubType; 
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

原型式继承

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"); 
var yetAnotherPerson = object(person); 
yetAnotherPerson.name = "Linda"; 
yetAnotherPerson.friends.push("Barbie"); 
alert(person.friends); //"Shelby,Court,Van,Rob,Barbie"

寄生式继承

function createAnother(original){ 
 var clone = object(original); //通过调用函数创建一个新对象
 clone.sayHi = function(){ //以某种方式来增强这个对象
 alert("hi"); 
 }; 
 return clone; //返回这个对象
}

组合寄生式继承

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); //第二次调用 SuperType() 
 this.age = age; 
} 
SubType.prototype = new SuperType(); //第一次调用 SuperType() 
SubType.prototype.constructor = SubType; 
SubType.prototype.sayAge = function(){ 
 alert(this.age); 
};