gcd.js

let test = [[3, [666, 123, 57, 191919, 2]]];

function gcd(a, b) {
  while (true) {
    if (a !== 0 && b !== 0) {
      if (a > b) {
        a = a % b;
      } else {
        b = b % a;
      }
    } else {
      return a + b;
    }
  }
}

function generalizedGCD(num, arr) {
  if (arr.length < 1) {
    return 1;
  }
  if (arr.length === 1) {
    return arr[0];
  }
  let _gcd = 0;
  for (let i = 0; i < arr.length - 1; i++) {
    if (arr[i] <= 1 || arr[i + 1] <= 1) {
      return 1;
    }
    _gcd = _gcd ? gcd(_gcd, arr[i + 1]) : gcd(arr[i], arr[i + 1]);
  }
  return _gcd;
}

test.forEach(el => console.log(generalizedGCD(...el)));