greater common divisor

gcd.js

function gcd (a, b) {
  if (a === b) {
    return a
  }

  const major = a > b ? a : b
  const minor = a > b ? b : a

  for (let i = minor; i > 0; --i) {
      if (major % i === 0 && minor % i === 0) {
          break;
      }
  }

  return i
}