between-two-sets.js

function getTotalX(a, b) {

  function lcm(a, b) {
    return a * b / gcd(a, b)
  }

  function gcd(a, b) {
    // Euclid's division algorithm
    let t
    while (b !== 0) {
      t = b
      b = a % b
      a = t
    }
    return a
  }

  let l = a.reduce(lcm),
    g = b.reduce(gcd),
    c = 0

  for (let i = l; i < g + 1; i += l) {
    if (g % i === 0) {
      ++c
    }
  }

  return c
}

console.log(getTotalX([2, 6], [24, 36]))
console.log(getTotalX([2, 4], [16, 32, 96]))