原型链与继承方式

1.原型继承，简单，但是原型对象的所有属性被所有实例共享，例如子类对color进行修改，其他的也会变。

function Parent(name, age){
  this.name = name;
  this.age = 24;
  this.getName = function (){
    return this.name;
  };
  this.color = ['ff','22'];
}
Parent.prototype.getAge = function (){
  return this.age;
}

function Son(name){
  this.name = name;
}
Son.prototype = new Parent();
let son1 = new Son('one');
let son2 = new Son('two');
son1.color.push('333');
console.log(son2.name);
console.log(son1.color);//["ff", "22", "333"]
console.log(son2.color);//["ff", "22", "333"]

2.构造函数继承，只会继承实例属性，不会继承原型属性

function Parent(name,age){
  this.name = name;
  this.age = age;
  this.getAge = function(){
    return this.age;
  }
}
Parent.prototype.getName = function(){
  return this.name;
}
Parent.prototype.sex = '男';

function Son(name,sex){
  this.name = name;
  this.sex = sex;
  Parent.call(this, name ,24);
}
let son = new Son('小仙女','女');
console.log(son.name);
console.log(son.sex);
console.log(son.getAge());
console.log(son.getName());  // undefined

3. 组合继承，会继承原型和实例的属性，但是会两次调用Parent，生成两份父类实例

function Parent(name,age){
  this.name = name;
  this.age = age;
  this.getAge = function(){
    return this.age;
  }
}
Parent.prototype.getName = function(){
  return this.name;
}
Parent.prototype.sex = '男';

function Son(name,sex,age){
  this.name = name;
  this.sex = sex;
  Parent.call(this, name ,age);
}

Son.prototype = new Parent(); 

let son = new Son('小仙女','女',22); 
console.log(son.name); 
console.log(son.sex);
console.log(son.getAge());
console.log(son.getName());

4. 寄生组合继承，比较完美

 function Parent(name,age){
  this.name = name;
  this.age = age;
  this.getAge = function(){
    return this.age;
  }
}
Parent.prototype.getName = function(){
  return this.name;
}
Parent.prototype.sex = '男';

function Son(name,sex,age){
  this.name = name;
  this.sex = sex;
  Parent.call(this, name ,age);
}
//复制一份父原型，Son的prototype指向复制的父，constructor指向Son构造函数
Son.prototype = Object.create(Parent.prototype);
Son.prototype.constructor = Son;

let son = new Son('小仙女','女',22); 
console.log(son.name); 
console.log(son.sex);
console.log(son.getAge());
console.log(son.getName());