class.js

'use strict';

// Object-oriendted programming
// class: template
// object: instance of a class
// JavaScript classes
// - introduced in ES6
// - syntactical sugar over prototype-based inheritance

// 1. Class declarations
class Person {
 // constructior
 constructor(name, age) {
 // fields
 this.name = name;
 this.age = age;
 }

 // methods
 speak() {
 console.log(`${this.name}: hello!`);
 }
}

const sill = new Person('sill', 20);
console.log(sill.name);
console.log(sill.age);
sill.speak();

// 2. Getter and setter
class User {
 constructor(firstName, lastName, age) {
 this.firstName = firstName;
 this.lastName = lastName;
 this.age = age;
 }

 get age() {
 return this._age;
 }

 set age(value) {
 // if(value < 0) {
 // throw Error('age can not be negative');
 // }
 this._age = value < 0 ? 0 : value;
 }
}

const user1 = new User('Steve', 'Job', -1);
console.log(user1.age);

// 3. Fields (public, private)
// Too soon!
// https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Classes/Private_class_fields
class Experiment {
 publicField = 2;
 #privateField = 0;
}
const experiment = new Experiment();
console.log(experiment.publicField);
console.log(experiment.privateField);

// 4. Static properties and methods
// Too soon!
class Article {
 static publisher = 'Dream Coding';
 constructor(articleNumber) {
 this.articleNumber = articleNumber;
 }

 static printPublisher() {
 console.log(Article.publisher);
 }
}

const article1 = new Article(1);
const article2 = new Article(2);
console.log(Article.publisher);
Article.printPublisher();

// 5. Inheritance
// a way for one class to extend another class.
class Shape {
 constructor(width, height, color) {
 this.width = width;
 this.height = height;
 this.color = color;
 }

 draw() {
 console.log(`drawing ${this.color} color of`);
 }

 getArea() {
 return this.width * this.height;
 }
}

class Rectangle extends Shape {}
class Triangle extends Shape {
 draw() {
 super.draw(); // 부모에 사용된 draw 메소드도 호출!
 console.log('triangle!');
 }
 getArea() {
 return (this.width * this.height) / 2;
 }
}

const rectangle = new Rectangle(20, 20, 'blue');
rectangle.draw();
console.log(rectangle.getArea());
const triangle = new Triangle(20, 20, 'red');
triangle.draw();
console.log(triangle.getArea());

// 6. Class checking: instanceOf
console.log(rectangle instanceof Rectangle); // true
console.log(triangle instanceof Rectangle); // false
console.log(triangle instanceof Triangle); // true
console.log(triangle instanceof Shape); // true
console.log(triangle instanceof Object); // true