Javascript如何实现继承？

构造继承

function SuperType() { this.colors = ['red', 'green', 'blue'] } function ChildType() { SuperType.call(this); } let instance1 = new ChildType(); instance1.colors.push('yellow'); console.log(instance1.colors); // ["red", "green", "blue", "yellow"] let instance2 = new ChildType(); console.log(instance2.colors); // ["red", "green", "blue"]

通过使用call()方法，我们实际上是在新创建的ChildType实例的环境下调用了SuperType，这样就会在新的ChildType的实例上执行SuperType中的初始化代码，这样每个实例都会有自己的colors属性副本。而借助构造函数相比于借用原型链的一大优势就是，子类型构造函数可以向超类型构造函数传递参数。

function SuperType(name) { this.name = name; } function ChildType(name) { SuperType.call(this, name); } let instance1 = new ChildType('Nick'); console.log(instance1.name); // 'Nick'

原型继承

Dog.prototype = Object.create(Cat.prototype);// 寄生继承 // Object.create()用于创建一个空对象，并把该对象的[[Prototype]]链接到Cat.prototype

实例继承

var Base = function() { this.level = 1; this.name = "base"; this.toString = function(){ return "base"; }; }; Base.CONSTANT = "constant"; var Sub = function() { var instance = new Base(); instance.name = "sub"; return instance; };

优点：是父类的对象，并且使用new构造对象和不使用new构造对象，都可以获得相同的效果。

缺点：生成的对象实质仅仅是父类的实例，并非子类的对象；不支持多继承。 拷贝继承

var Base = function() { this.level = 1; this.name = "base"; this.toString = function(){ return "base"; }; }; Base.CONSTANT = "constant"; var Sub = function() { var base = new Base(); for(var i in base) Sub.prototype[i] = base[i]; Sub.prototype["name"] = "sub"; };

混合继承 构造函数继承和原型链继承结合

function Cat(n,c){ this.name = n; this.color = c; this.say = function (){ console.log('卖萌~'); } return {a:1,b:2} } Cat.prototype.type = 'animal'; Cat.prototype.skill = function (){ alert('抓老鼠'); } function Dog(f,n,c){ this.food = f; Cat.call(this,n,c);//构造函数继承 } Dog.prototype = Object.create(Cat.prototype);//原型继承 Dog.prototype.constructor = Dog;//手动指正构造器 var dog1 = new Dog('shi','小花','red'); console.log( dog1.food ); console.log( dog1.name ); dog1.say(); dog1.skill();