随手记之继承的几种实现方式

1.原型链

基本思想：利用原型让一个引用类型继承另外一个引用类型的属性和方法。
构造函数，原型，实例之间的关系：每个构造函数都有一个原型对象，原型对象包含一个指向构造函数的指针，而实例都包含一个指向原型对象的内部指针。

function SuperType() {
    this.property = true;
}
SuperType.prototype.getSuperValue = function() {
    return this.property;
}
function subType() {
    this.property = false;
}
//继承了SuperType
SubType.prototype = new SuperType();
SubType.prototype.getSubValue = function (){
    return this.property;
}
var instance = new SubType();
console.log(instance.getSuperValue());//true

2.借用构造函数

基本思想：在子类型构造函数的内部调用超类构造函数，通过使用call()和apply()方法可以在新创建的对象上执行构造函数。

function SuperType() {
    this.colors = ["red","blue","green"];
}
function SubType() {
    SuperType.call(this);//继承了SuperType
}
var instance1 = new SubType();
instance1.colors.push("black");
console.log(instance1.colors);//"red","blue","green","black"
var instance2 = new SubType();
console.log(instance2.colors);//"red","blue","green

3.组合继承

基本思想：将原型链和借用构造函数的技术组合在一块，从而发挥两者之长的一种继承模式。

function SuperType(name) {
this.name = name;
    this.colors = ["red","blue","green"];
}
SuperType.prototype.sayName = function() {
    console.log(this.name);
}
function SubType(name, age) {
    SuperType.call(this,name);//继承属性
    this.age = age;
}
//继承方法
SubType.prototype = new SuperType();
SubType.prototype.constructor = Subtype;
SubType.prototype.sayAge = function() {
    console.log(this.age);
}
var instance1 = new SubType("EvanChen",18);
instance1.colors.push("black");
console.log(instance1.colors);//"red","blue","green","black"
instance1.sayName();//"EvanChen"
instance1.sayAge();//18
var instance2 = new SubType("EvanChen666",20);
console.log(instance2.colors);//"red","blue","green"
instance2.sayName();//"EvanChen666"
instance2.sayAge();//20

4.原型式继承

基本想法：借助原型可以基于已有的对象创建新对象，同时还不必须因此创建自定义的类型。
原型式继承的思想可用以下函数来说明：

function object(o) {
    function F(){}
    F.prototype = o;
    return new F();
}

var person = {
    name:"EvanChen",
    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");
console.log(person.friends);//"Shelby","Court","Van","Rob","Barbie"

5.寄生式继承

基本思想：创建一个仅用于封装继承过程的函数，该函数在内部以某种方式来增强对象，最后再像真正是它做了所有工作一样返回对象。

function createAnother(original) {
    var clone = object(original);
    clone.sayHi = function () {
    alert("hi");
    };
    return clone;
}
var person = {
    name:"EvanChen",
    friends:["Shelby","Court","Van"];
};
var anotherPerson = createAnother(person);
anotherPerson.sayHi();///"hi"

6.寄生组合式继承

基本思想：通过借用函数来继承属性，通过原型链的混成形式来继承方法
其基本模型如下所示：

function inheritProperty(subType, superType) {
    var prototype = object(superType.prototype);//创建对象
    prototype.constructor = subType;//增强对象
    subType.prototype = prototype;//指定对象
}

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;
}
inheritProperty(SubType,SuperType);
    SubType.prototype.sayAge = function() {
    alert(this.age);
}