https://codeperfectplus.com/10-days-of-javascript-day-5

Inheritance.js

class Rectangle {
    constructor(w, h) {
        this.w = w;
        this.h = h;
    }
}

Rectangle.prototype.area = function () {
    return this.w * this.h;
}
class Square extends Rectangle {
    constructor(s) {
        super();
        this.h = s;
        this.w = s;
    }
}