借用构造函数,借助call或apply,使用Superclass构造函数,缺少函数复用
Superclass.call(this, name)
这里使Subclass继承了Superclass的实例属性this.name
,但无法使用Superclass原型链上的属性及方法test.say()
会抛出一个test.try is not a function
异常。
function applyOrCall() {
function Superclass(name = 'default') {
this.name = name;
}
Superclass.prototype.try = function () {
console.log('ok');
};
function Subclass(age = 22, name) {
this.age = age;
Superclass.call(this, name);
this.say = function () {
console.log(`this.name=${this.name}...this.age=${this.age}`);
};
}
const test = new Subclass(23);
test.say();
console.log(`test instanceof Subclass`, test instanceof Subclass);
console.log(`test instanceof Superclass`, test instanceof Superclass);
console.log(test.__proto__.constructor);
console.log(Subclass.prototype.constructor);
}
applyOrCall();
原型链继承,使用prototype指向Superclass对象,子类无法给父类传递参数,无法使用字面量添加新方法,所有子类对象共享父类所有方法和属性(引用类型),Subclass.prototype = new Superclass()
此时Subclass原型对象拥有Superclass实例,并且被所有Subclass实例共享。
function prototype() {
function Superclass(name = 'default') {
this.name = name;
this.colors = ['r', 'y'];
}
function Subclass(age = 22) {
this.age = age;
this.say = function () {
console.log(`this.name=${this.name}...this.age=${this.age}`);
};
}
Subclass.prototype = new Superclass();
Subclass.prototype.constructor = Subclass;
const test = new Subclass(23);
const test1 = new Subclass(24);
test.colors.push('b');
console.log(test.colors);
console.log(test1.colors);
test.say();
test1.say();
console.log(`test instanceof Subclass`, test instanceof Subclass);
console.log(`test instanceof Superclass`, test instanceof Superclass);
console.log(test.__proto__.constructor);
console.log(Subclass.prototype.constructor);
}
prototype();
组合继承,prototype+call/apply,借用构造函数对实例属性继承,prototype对共享方法继承,会调用两次父类构造函数,第一次Subclass.prototyp= new Superclass();
此时Subclass原型对象为Superclass实例,并且被所有Subclass实例共享,当调用new Subclass()
时Superclass.call(name)
第二次父类构造函数被调用,此时Superclass继承的实例属性覆盖原型链上继承的父类属性。
function prototypeApplyCall() {
function Superclass(name = 'default') {
this.name = name;
}
Superclass.prototype.say = function () {
console.log(this.name);
};
function Subclass(age = 22, name) {
this.age = age;
Superclass.call(name);
}
Subclass.prototype = new Superclass();
Subclass.prototype.constructor = Subclass;
const test = new Subclass(23);
test.say();
console.log(`test instanceof Subclass`, test instanceof Subclass);
console.log(`test instanceof Superclass`, test instanceof Superclass);
console.log(test.__proto__.constructor);
console.log(Subclass.prototype.constructor);
}
prototypeApplyCall();
ES6 Class继承,必须在子类`constructor`中最先调用`super()`方法
function Class() {
class Superclass {
constructor(name = 'default') {
this.name = name;
}
}
class Subclass extends Superclass {
constructor(age = 22, name) {
super(name);
this.age = age;
}
say() {
console.log(`this.name=${this.name}...this.age=${this.age}`);
}
}
const test = new Subclass(23);
test.say();
console.log(`test instanceof Subclass`, test instanceof Subclass);
console.log(`test instanceof Superclass`, test instanceof Superclass);
console.log(test.__proto__.constructor);
console.log(Subclass.prototype.constructor);
}
Class();
Node util.inherits;`inherits` 的主要实现还是基于原型链
ctor.super_ = superclass;
Object.setPrototypeOf(subclass.prototype, superclass.prototype);
function inherits() {
function Superclass(name = 'default') {
this.name = name;
}
function Subclass(age = 22, name) {
this.age = 22;
Superclass.call(this, name);
this.say = function () {
console.log(`this.name=${this.name}...this.age=${this.age}`);
};
}
require('util').inherits(Subclass, Superclass);
const test = new Subclass(23);
test.say();
console.log(`test instanceof Subclass`, test instanceof Subclass);
console.log(`test instanceof Superclass`, test instanceof Superclass);
console.log(test.__proto__.constructor);
console.log(Subclass.prototype.constructor);
}
inherits();