A first introduction to object-oriented JavaScript

js object-oriented knowledge is the most basic entry-level knowledge point. The following is a detailed introduction to js object-oriented knowledge through the example code of this article. Friends who are interested can learn together

Class Declaration

1. Constructor

##

function Animal() {
 this.name = 'name'
}
// 实例化
new Animal()

2. ES6 class

class Animal {
 constructor() {
  this.name = 'name'
 }
}
// 实例化
new Animal()

Class inheritance

1. Implement inheritance with the help of constructor

Principle: Change the this pointer of the subclass when running, but the attributes on the prototype chain of the parent class are not inherited, which is incomplete inheritance

function Parent() {
 this.name = 'Parent'
}
Parent.prototype.say = function(){
 console.log('hello')
}
function Child() {
 Parent.call(this)
 this.type = 'Child'
}
console.log(new Parent())
console.log(new Child())

2. Implement inheritance with the help of prototype chain

Principle: Prototype chain, but if an attribute in the parent class is changed in a subclass instance, the attribute in other instances will also change the subclass. , it is also incomplete inheritance

function Parent() {
 this.name = 'Parent'
 this.arr = [1, 2, 3]
}
Parent.prototype.say = function(){
 console.log('hello')
}
function Child() {
 this.type = 'Child'
}
Child.prototype = new Parent()
let s1 = new Child()
let s2 = new Child()
s1.arr.push(4)
console.log(s1.arr, s2.arr)
console.log(new Parent())
console.log(new Child())
console.log(new Child().say())

3. Constructor + prototype chain

Best Practice

// 父类
function Parent() {
 this.name = 'Parent'
 this.arr = [1, 2, 3]
}
Parent.prototype.say = function(){
 console.log('hello')
}
// 子类
function Child() {
 Parent.call(this)
 this.type = 'Child'
}
// 避免父级的构造函数执行两次，共用一个 constructor
// 但是无法区分实例属于哪个构造函数
// Child.prototype = Parent.prototype
// 改进：创建一个中间对象，再修改子类的 constructor
Child.prototype = Object.create(Parent.prototype)
Child.prototype.constructor = Child
// 实例化
let s1 = new Child()
let s2 = new Child()
let s3 = new Parent()
s1.arr.push(4)
console.log(s1.arr, s2.arr) // [1, 2, 3, 4] [1, 2, 3]
console.log(s2.constructor) // Child
console.log(s3.constructor) // Parent
console.log(new Parent())
console.log(new Child())
console.log(new Child().say())

The above is the detailed content of A first introduction to object-oriented JavaScript. For more information, please follow other related articles on the PHP Chinese website!