JS [Class]

Class
-template
-declare once
-no data in
-틀

Object
- instance of a class
- created many times
- data in

'use strict'

// 1. Class declartions

class person{

    //constructor

    constructor(name,age){

        //fields

        this.name=name;

        this.age=age;

    }

    // methods

    speak(){

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

    }

}

const ellie = new person('ellie',20);

ellie.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){

            value=0;

        }

    this._age=value<0 ? 0: value;

    }

}

const user1 = new User('Steve','Job',-1);

console.log(user1.age);

// 3. Fields (public, private)

class Experiment{

    publicField=2;

    #privateField=0;

}

const Experiment = new Experiment();

console.log(Experiment.publicField);

// class 밖에서는 private에 접근 불가

// 최근에 나옴

// 4. static properties and methods

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();

// 들어오는 값에 상관없이 같은 내용을 출력할 때 사용

// 메모리 사용을 줄일 수 있음

// 5. 상속 & 다향성

// 공통적인 특성들을 클래스로 정리

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 width * this.height;

    }

}

class Rectangle extends Shape {}

class Triangle extends Shape{

    draw(){

        super.draw();

        console.log('semo');

    }

    // 오버라이딩

    getArea(){

        return this.width * this.height /2;

    }

}

const rectangle = new Rectangle(20,20,'blue');

rectangle.draw();

const triangle = new Triangle(20,20,'red');

triangle.draw();

console.log(triangle.getArea());

// 6. Class checking : instanceOf

// 왼쪽의 Object가 오른쪽의 class에 속하는지 확인

console.log(rectangle instanceof Rectangle);