3.classes.js

// Class declarations
class Square {
    constructor(length) {
        this.length = length;
    }

    get area() {
        return this.length * this.length;
    }

    set area(value) {
        this.area = value;
    }
}

// Class expression
const square = class Square {
    constructor(length) {
        this.length = length;
    }

    get area() {
        return this.length * this.length;
    }

    set area(value) {
        this.area = value;
    }
}

// Inheritance
class Vehicle {
    constructor(name) {
        this.name = name;
    }

    start() {
        console.log(`${this.name} vehicle started`);
    }
}

class Car extends Vehicle {
    start() {
        console.log(`${this.name} car started`);
    }
}

const car = new Car('BMW');
console.log(car.start()); // BMW car started