add classes to commonjs system

app.js

const calc = require('./calculator.js');
const myCalculator = new calc.myCalc();

console.log(myCalculator.summ(7, 8));
console.log(myCalculator.diff(4, 10));

console.log(myCalculator.divv(4, 5));
console.log(myCalculator.mult(4, 9));

calculator.js

const superCalc = require('./supercalculator.js');


class Calc extends superCalc.mySuperCalc{  
  summ(a, b) {
    return a + b;
  }

  diff(a, b) {
    return a - b;
  }
}

exports.myCalc = Calc;

supercalculator.js

class SuperCalc {  
  mult(a, b) {
    return a * b;
  }

  divv(a, b) {
    return a / b;
  }
} 


exports.mySuperCalc = SuperCalc;