类方法与对象方法

Posted 2020-08-09 晴天的故事

js函数式编程确实比很多强语言使用灵活得多，今天抽了点时间玩下类与对象方法调用优先级别，顺便回顾下继承

暂时把原型引用写成继承

 

先看看简单的两个继承

var Parent = function(){};
var b = new  Parent();
Object.defineProperty(b,"Name",{value:"John",writable:true});
var A = function(){};
A.prototype= b;
var a = new Child();
alert(a.Name); //John

 

再加点料，给父类加上类方法

var B = function(){this.getName=function(){};
var b = new B();
Object.defineProperty(b,"Name",{value:"John",writable:true});
B.prototype.getName = function(){return "Parent said:" + this.Name;};
B.prototype.setName = function(value){this.Name = value;};
var A = function(){};
A.prototype= b;
var a = new A();
alert(a.Name); // Parent said John
alert(a.getName()); //Parent said John
a.setName("Keven");
alert(a.getName());//Parent said Keven

 

子类继承并使用了父类原型的方法和属性, 也能通过父类提供的方法修改继承的属性值，再来加点料

 

var Parent = function(){this.getName=function(){return "Parent child object said:"+this.Name};};
var b = new Parent();
Object.defineProperty(b,"Name",{value:"John",writerable:true});
Parent.prototype.getName = function(){return "Parent sard:" + this.Name;};
Parent.prototype.setName = function(value){this.Name = value;};
var A = function(){};
A.prototype= b;
var a = new A();

alert(a.Name); // Parent said John
alert(a.getName()); //Parent said John
a.setName("Keven");
alert(a.getName());//Parent child object said John

What, 最后一条输出没有出来Keven, 而是调用了对象的方法，此处可以看出对象方法优先于原型方法调用，当对象方法没有找到时会向上层原型查找

 

再来看看类方法，再来加点料，Parent类加上getName方法，胃口有点重

var Parent = function(){this.getName=function(){return "Parent child object said:"+this.Name};};
var b = new Parent();
Object.defineProperty(b,"Name",{value:"John",writerable:true});
Parent.prototype.getName = function(){return "Parent sard:" + this.Name;};
Parent.getName = fucntion(){return this.Name;};
Parent.prototype.setName = function(value){this.Name = value;};
var A = function(){};
A.prototype= b;
var a = new A();
alert(a.Name); // Parent said John
alert(a.getName()); //Parent said John
a.setName("Keven");
alert(a.getName());//Parent child object said Keven
alert(A.prototype.Name); //John
alert(A.getName()) // type error, undefine is not a function

最后一条报错，A并没有继承Parent的getName方法，此处可以理解Parent.getName为静态方法，不会被子类继承

var Parent = function(){this.getName=function(){return "Parent child object said:"+this.Name};};
var b = new Parent();
Object.defineProperty(b,"Name",{value:"John",writerable:true});
Parent.prototype.getName = function(){return "Parent sard:" + this.Name;};
Parent.getName = fucntion(){return this.Name;};
Parent.prototype.setName = function(value){this.Name = value;};
var A = function(){this.getName=function(){return "A object said:"+this.Name};};
A.prototype= b;
var a = new A();
alert(a.Name); // Parent said John
a.setName("Keven");
alert(a.getName());//A object said Keven
alert(A.prototype.Name); //John
alert(A.getName()) // type error, undefine is not a function