fractions.js

function Fraction(n, d) {
  this.n = n;
  if (d) this.d = d;
  else this.d = 1;
}

Fraction.prototype.reciprocal = function() {
  return {n: this.d, d: this.n};
}

function gcf(x, y) {
  if (y > x) {
    return gcf(y, x);
  }
  if (!y) {
    return x;
  }
  var r = x % y;
  return gcf(y, r);
}

Fraction.prototype.reduce = function() {
  if (!this.d || this.n % 1 || this.d % 1) return {success: false, error: 'invalid fraction'};
  var that = new Fraction(this.n, this.d);
  if (that.d < 0) {
    that.n *= -1;
    that.d *= -1;
  }
  var factor = 2;
  while (gcf(Math.abs(that.n), Math.abs(that.d)) != 1) {
    if (!(Math.abs(that.n) % factor) && !(Math.abs(that.d) % factor)) {
      that.n /= factor;
      that.d /= factor;
    }
    else factor++;
  }
  return that;
}

Fraction.prototype.add = function(frac2) {
  var that = new Fraction(this.n, this.d).reduce();
  frac2 = frac2.reduce();
  return new Fraction(that.n * frac2.d + frac2.n * that.d, that.d * frac2.d).reduce();
}

Fraction.prototype.subtract = function(frac2) {
  var that = new Fraction(this.n, this.d).reduce();
  frac2 = frac2.reduce();
  frac2.n *= -1;
  return new Fraction(that.n * frac2.d + frac2.n * that.d, that.d * frac2.d).reduce();
}

Fraction.prototype.gt = function(frac2) {
  return this.n * frac2.d > this.d * frac2.n;
}

Fraction.prototype.lt = function(frac2) {
  return this.n * frac2.d < this.d * frac2.n;
}

Fraction.prototype.equals = function(frac2) {
  return this.n * frac2.d == this.d * frac2.n;
}