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static

static

class User {
  static staticMethod() {
    alert(this === User);
  }
}

User.staticMethod(); // true

class User { }

User.staticMethod = function() {
  alert(this === User);
};

User.staticMethod(); // true

User.staticMethod() this User

Article

Article.compare

class Article {
  constructor(title, date) {
    this.title = title;
    this.date = date;
  }

  static compare(articleA, articleB) {
    return articleA.date - articleB.date;
  }
}

// 
let articles = [
  new Article("HTML", new Date(2019, 1, 1)),
  new Article("CSS", new Date(2019, 0, 1)),
  new Article("JavaScript", new Date(2019, 11, 1))
];

articles.sort(Article.compare);

alert( articles[0].title ); // CSS

Article.compare class

titledate

constructor

Article.createTodays()

class Article {
  constructor(title, date) {
    this.title = title;
    this.date = date;
  }

  static createTodays() {
    //  this = Article
    return new this("Today's digest", new Date());
  }
}

let article = Article.createTodays();

alert( article.title ); // Today's digest

Article.createTodays() class

          //  Article 
//  id 
Article.remove({id: 12345});
        

          // ...
article.createTodays(); /// Error: article.createTodays is not a function
        

JavaScript Chrome

static

class Article {
  static publisher = "Levi Ding";
}

alert( Article.publisher ); // Levi Ding

Article

Article.publisher = "Levi Ding";

Animal.compare Animal.planet Rabbit.compare Rabbit.planet

class Animal {
  static planet = "Earth";

  constructor(name, speed) {
    this.speed = speed;
    this.name = name;
  }

  run(speed = 0) {
    this.speed += speed;
    alert(`${this.name} runs with speed ${this.speed}.`);
  }

  static compare(animalA, animalB) {
    return animalA.speed - animalB.speed;
  }

}

//  Animal
class Rabbit extends Animal {
  hide() {
    alert(`${this.name} hides!`);
  }
}

let rabbits = [
  new Rabbit("White Rabbit", 10),
  new Rabbit("Black Rabbit", 5)
];

rabbits.sort(Rabbit.compare);

rabbits[0].run(); // Black Rabbit runs with speed 5.

alert(Rabbit.planet); // Earth

Rabbit.compare Animal.compare

extends Rabbit [[Prototype]] Animal

[]

Rabbit extends Animal [[Prototype]]

Rabbit Animal
Rabbit.prototype Animal.prototype

class Animal {}
class Rabbit extends Animal {}

// 
alert(Rabbit.__proto__ === Animal); // true

// 
alert(Rabbit.prototype.__proto__ === Animal.prototype); // true

Article.compare(article1, article2) factory Article.createTodays()

static

          class MyClass {
  static property = ...;

  static method() {
    ...
  }
}
        

          MyClass.property = ...
MyClass.method = ...
        

class B extends A B prototype AB.[[Prototype]] = A B A

Object.prototype hasOwnProperty

class Rabbit {
  constructor(name) {
    this.name = name;
  }
}

let rabbit = new Rabbit("Rab");

// hasOwnProperty  Object.prototype
alert( rabbit.hasOwnProperty('name') ); // true

"class Rabbit extends Object" "class Rabbit"

          class Rabbit extends Object {
  constructor(name) {
    this.name = name;
  }
}

let rabbit = new Rabbit("Rab");

alert( rabbit.hasOwnProperty('name') ); // Error
        

constructor super() "this"

class Rabbit extends Object {
  constructor(name) {
    super(); //  constructor
    this.name = name;
  }
}

let rabbit = new Rabbit("Rab");

alert( rabbit.hasOwnProperty('name') ); // true

"class Rabbit extends Object" class Rabbit

extends

"prototype"

class Rabbit extends Object

class Rabbit extends Object {}

alert( Rabbit.prototype.__proto__ === Object.prototype ); // (1) true
alert( Rabbit.__proto__ === Object ); // (2) true

Rabbit Rabbit Object

class Rabbit extends Object {}

//  Object.getOwnPropertyNames
alert ( Rabbit.getOwnPropertyNames({a: 1, b: 2})); // a,b

extends Object Rabbit.__proto__ Object

class Rabbit {}

alert( Rabbit.prototype.__proto__ === Object.prototype ); // (1) true
alert( Rabbit.__proto__ === Object ); // (2) false (!)
alert( Rabbit.__proto__ === Function.prototype ); // true

// errorRabbit 
alert ( Rabbit.getOwnPropertyNames({a: 1, b: 2})); // Error

Rabbit Object

Function.prototype call bind Object Object.__proto__ === Function.prototype

[]

class Rabbit	class Rabbit extends Object
	constructor `super()`
`Rabbit.__proto__ === Function.prototype`	`Rabbit.__proto__ === Object`