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Javascript的ES5,ES6的7种继承

arzh 人气:0

众所周知,在ES6之前,前端是不存在类的语法糖,所以不能像其他语言一样用extends关键字就搞定继承关系,需要一些额外的方法来实现继承。下面就介绍一些常用的方法,红宝书已经概括的十分全面了,所以本文基本就是对红宝书继承篇章的笔记和梳理。

原型链继承

function Parent() {
    this.name = 'arzh'
}
Parent.prototype.getName = function () {
    console.log(this.name)
}
function Child() {
}
//主要精髓所在
Child.prototype = new Parent()
Child.prototype.constructor = Child
var arzhChild = new Child()
arzhChild.getName() // 'arzh'

原型链继承缺点:

1.每个实例对引用类型属性的修改都会被其他的实例共享

function Parent() {
    this.names = ['arzh','arzh1'];
}
function Child() {
}
//主要精髓所在
Child.prototype = new Parent()
Child.prototype.constructor = Child
var arzhChild2 = new Child()
arzhChild2.names.push('arzh2')
console.log(arzhChild2.names) //[ 'arzh', 'arzh1', 'arzh2' ]
var arzhChild3 = new Child()
arzhChild3.names.push('arzh3')
console.log(arzhChild3.names) //[ 'arzh', 'arzh1', 'arzh2', 'arzh3' ]

2.在创建Child实例的时候,无法向Parent传参。这样就会使Child实例没法自定义自己的属性(名字)

借用构造函数(经典继承)

function Parent() {
    this.names = ['arzh','arzh1']
}
function Child() {
    Parent.call(this)
}
var arzhChild2 = new Child()
arzhChild2.names.push('arzh2')
console.log(arzhChild2.names) //[ 'arzh', 'arzh1', 'arzh2' ]
var arzhChild3 = new Child()
arzhChild3.names.push('arzh3')
console.log(arzhChild3.names) //[ 'arzh', 'arzh1', 'arzh3' ]

优点:

function Parent(name) {
    this.name = name
}
function Child(name) {
    Parent.call(this, name)
}
var arzhChild = new Child('arzh');
console.log(arzhChild.name); // arzh
var arzhChild1 = new Child('arzh1');
console.log(arzhChild1.name); // arzh1

缺点:

组合式继承(原型链继承和借用构造函数合并)

function Parent(name) {
    this.name = name
    this.body = ['foot','hand']
}
function Child(name, age) {
    Parent.call(this, name)
    this.age = age
}
Child.prototype = new Parent()
Child.prototype.constructor = Child
var arzhChild1 = new Child('arzh1', '18')
arzhChild1.body.push('head1')
console.log(arzhChild1.name,arzhChild1.age) //arzh1 18
console.log(arzhChild1.body) //[ 'foot', 'hand', 'head1' ]
var arzhChild2 = new Child('arzh2', '20')
arzhChild2.body.push('head2')
console.log(arzhChild2.name,arzhChild2.age) //arzh2 20
console.log(arzhChild2.body) //[ 'foot', 'hand', 'head2' ]

优点:

缺点:

原型式继承

复制传入的对象到创建对象的原型上,从而实现继承

function createObj(o) {
    function F(){}
    F.prototype = o;
    return new F();
}
var person = {
    name : 'arzh',
    body : ['foot','hand']
}
var person1 = createObj(person)
var person2 = createObj(person)
console.log(person1) //arzh
person1.body.push('head') 
console.log(person2) //[ 'foot', 'hand', 'head' ]

缺点: 同原型链继承一样,每个实例对引用类型属性的修改都会被其他的实例共享

寄生式继承

我们可以使用Object.create来代替上述createObj的实现,原理基本上是一样的。寄生式继承其实就是在createObj的内部以某种形式来增强对象(这里的增强可以理解为添加对象的方法),最后返回增强之后的对象。

function createEnhanceObj(o) {
    //代替原型式继承的createObj
    var clone = Object.create(o)
    clone.getName = function () {
        console.log('arzh')
    }
    return clone;
}

通过createEnhanceObj就可以在创建对象的时候,把对象方法也通过此种方式继承。

缺点: 同借用构造函数一样,无法复用父类函数,每次创建对象都会创建一遍方法

寄生组合式继承

不需要为了子类的原型而多new了一次父类的构造函数,如Child.prototype = new Parent() 只需要复制父类原型的一个副本给子类原型即可

function inheritPrototype(Parent, Child){
	Child.prototype = Object.create(Parent.prototype) //创建父类原型的一个副本,把副本赋值给子类原型
	Child.prototype.constructor = Child;
}
function Parent(name) {
    this.name = name
}
Parent.prototype.getName = function () {
    console.log(this.name)
}
function Child(color) {
    Parent.call(this, 'arzh')
    this.color = color
}
inheritPrototype(Parent, Child)
var arzhChild = new Child('red')
console.log(arzhChild.name) // 'arzh'

优点: 不必为了指定子类型的原型而调用父类型的构造函数

ES6继承

ES6支持通过类来实现继承,方法比较简单,代码如下

class Point {
    constructor(x, y) {
        this.x = x
        this.y = y
    }
    toString() {
        return this.x + '' + this.y
    }
}
class ColorPoint extends Point {
    constructor(x, y, color) {
        super(x, y) //调用父类的constructor(x, y)
        this.color = color
    }
    toString() {
        return this.color + ' ' + super.toString() // 调用父类的toString()
    }
}
var colorPoint = new ColorPoint('1', '2', 'red')
console.log(colorPoint.toString())  // red 12

总结

本篇文章就到这里了,希望能够给你带来帮助,也希望您能够多多关注的更多内容!     

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