js的继承

JavaScript的继承方式

function animal(name = "animal"){
    this.name = name;
    this.sleep = function(){
        console.log(this.name + '睡觉了' );
    } 
}         //父类

animal.prototype.eat = function(food){
    console.log(this.name + '正在吃' + food);
}

一、原型链继承
将父亲的实例作为子类的原型

function Cat(){
    Cat.prototype = new animal();
    Cat.prototype.name = 'Cat';
}

二、构造继承
使用父类的构造函数来增强子类实例，等于赋值父类的实例属性给子类

function Cat(name = 'Tom'){
   animal.call(this);
   this.name = name;
}

可以实现多继承，只是继承父类的实例属性和方法，不能继承原型属性/方法

三、实例继承
为父类实例添加新特性，作为子类实例返回

function Cat(name = 'Tom'){
   var instance = new animal();
   instance.name = name
   return instance;
}

实例是父类的实例，不是子类的

四、拷贝继承

function Cat(name = 'Tom'){
   var animal = new animal();
   for(var p in animal){
        Cat.prototype[p] = animal[p];
   }
   Cat.prototype.name = name;
}

需要枚举，受限，效率低

五、组合继承
通过调用父类的构造，继承父类的属性并保留传参的优点，然后通过把父类实例作为子类原型，实现函数复用

function People(name,age){
  this.name = name || 'wangxiao'
  this.age = age || 27
}
People.prototype.eat = function(){
  return this.name + this.age + 'eat sleep'
}
function Woman(name,age){
  People.call(this,name,age)
}
Woman.prototype = new People();
Woman.prototype.constructor = Woman;

let wonmanObj = new Woman(ren,27);
wonmanObj.eat(); 

六、寄生组合继承

//父类
function People(name,age){
  this.name = name || 'wangxiao'
  this.age = age || 27
}
//父类方法
People.prototype.eat = function(){
  return this.name + this.age + 'eat sleep'
}
//子类
function Woman(name,age){
  //继承父类属性
  People.call(this,name,age)
}
//继承父类方法
(function(){
  // 创建空类
  let Super = function(){};
  Super.prototype = People.prototype;
  //父类的实例作为子类的原型
  Woman.prototype = new Super();
})();
//修复构造函数指向问题
Woman.prototype.constructor = Woman;
let womanObj = new Woman();