Math Class (JavaScript)

// Math with Natural Numbers
function NMath(notNatural) {
  this.NOT_NATURAL = notNatural;
}
NMath.prototype = {
  ZERO_FACTORIAL: 1,
  // Triangle Number
  tri: function(n) {
    if (n < 0) {
      return this.NOT_NATURAL;
    }
    else if (n == 0) {
      return 0;
    }
    else {
      return n + this.tri(n - 1);
    }
  },
  // Factorial
  fac: function(n) {
    if (n < 0) {
      return this.NOT_NATURAL;
    }
    else if (n == 0) {
      return this.ZERO_FACTORIAL;
    }
    else {
      return n * this.fac(n - 1);
    }
  },
}

// Math with Whole Numbers
function ZMath() {
  NMath.call(this, -666);
};
ZMath.prototype = Object.create(NMath.prototype);
// Absolute Value
ZMath.prototype.abs = function(n) {
  return (n < 0) ? -n : n;
}

// Math with Rational Numbers
function QMath() {
  ZMath.call(this);
}
QMath.prototype = Object.create(ZMath.prototype);
// Triangle Number
QMath.prototype.tri = function(n) {
  if (n < 0) {
    return this.NOT_NATURAL;
  }
  else {
    return (n*(n+1))/2;
  }
}

// Quiz: What output does the following code produce?
var nMath = new NMath(-1);
var qMath = new QMath();
console.log(qMath.abs(qMath.NOT_NATURAL));
console.log(nMath.tri(5));
console.log(qMath.tri(10));
console.log(qMath.fac(3));
console.log(qMath.fac(-3));
console.log(nMath.tri(-1));
console.log(qMath.tri(-1));