function Rectangle(a, b) {
    this.a = a;
    this.b = b;
}

// jede Funktion besitzt einen Prototypen
Rectangle.prototype.getArea = function() {
    return this.a * this.b;
}

const r1 = new Rectangle(2, 3);
const r2 = new Rectangle(4, 5);

console.log(r1.getArea());
console.log(r2.getArea());