figuresClasses

class Shape
{
    constructor()
    {
        this._sides = [];
    };

    _setSide(sideId, sideLength)
    {
        this._sides[sideId] = sideLength;
    };

    _getSide(sideId)
    {
        return this._sides[sideId];
    };

    sidesInfo()
    {
        this._sides.forEach((it, id)=>{ console.log(`Side #${id} is ${it} long`); });
    };

    getPerimeter()
    {
        return this._sides.reduce((prev,cur)=>{return prev+cur;},0);
    };

    getArea()
    {
        return 0;
    };

    get name()
    {
        return this.constructor.name;
    }
}

class Rectangle extends Shape
{
    constructor(sideA, sideB)
    {
        super();
        this._setSide(0,sideA);
        this._setSide(1,sideB);
    };

    getPerimeter()
    {
        return super.getPerimeter() * 2;
    };

    getArea()
    {
        return this._getSide(0) * this._getSide(1);
    };
}

class Square extends Rectangle
{
    constructor(sideA)
    {
        super(sideA,sideA);
    };
};

class Triangle extends Shape
{
    constructor(sideA, sideB, sideC)
    {
        super();
        this._setSide(0,sideA);
        this._setSide(1,sideB);
        this._setSide(2,sideC);
    };

    getArea()
    {
        let p = this.getPerimeter() / 2;
        return Math.sqrt(p*(p-this._getSide(0))*(p-this._getSide(1))*(p-this._getSide(2)));
    };
}

let shapes =[new Rectangle(4,5), new Square(6), new Triangle(3,4,5)];
shapes.forEach((it,id)=>{console.log(`${id}. ${it.name} Perimeter: ${it.getPerimeter()} Area: ${it.getArea()}`);});