Greatest common divisor

gcd.js

/**
 * Returns the greatest common divisor of a and b
 * @param {number} a
 * @param {number} b
 * @returns {number}
 */
function gcd(a, b) {
  if (b == 0) {
    return a;
  } else {
    return gcd(b, a % b);
  }
}