class object 객체지향

class는 붕어빵 틀이라면 object는 붕어빵 속(팥, 크림, 치즈..)

 

1. Class declaration

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

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

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

private 변수는 함수 안에서만 읽어낼 수 있다

http://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference

class Experiment {
        publicField = 2;
        #privateField = 0;
    }
    const experiment = new Experiment(); 
    console.log(experiment.publicField); //2
    console.log(experiment.privateField); //undefined

 

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();

 

5. Inheritance

class Shape {
        constructor(width, height, color) {
            this.width = width;
            this.height = height;
            this.color = color;
        } //field

        draw() {
            console.log(`drawing ${this.color} color!`);
        } //method

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

    class Rectangle extends Shape {}
    class Triangle extends Shape {
        draw() {
            super.draw();
            console.log('🔺');
        }
        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