Leetcode 273 - Integer to English words - review the peer's JavaScript code

Leetcode273_IntegerToEnglishWords_codereview.js

/* 
Convert a non-negative integer to its english words representation. Given input is guaranteed to be less than 2^31 - 1.

For example,
123 -> "One Hundred Twenty Three"
12345 -> "Twelve Thousand Three Hundred Forty Five"
1234567 -> "One Million Two Hundred Thirty Four Thousand Five Hundred Sixty Seven"

less than 2 billion -> 
 */
  
const upToTwenty = ['', "One", "Two", "Three", "Four", "Five", "Six", "Seven", "Eight", "Nine", "Ten","Eleven", 
                    "Twelve", "Thirteen", "Fourteen", "Fifteen", "Sixteen", "Seventeen", "Eighteen", "Nineteen"];
  
const tens = ['', "Ten", "Twenty", "Thirty", "Forty", "Fifty", "Sixty", "Seventy", "Eighty", "Ninety"]
  
const thousands = ['', 'Thousand', 'Million', 'Billion'];

function numToWords(num) {
  
  // convert the input number to a string
  // if the number is bigger than 12 places
    // return 0 it would be too big
  if (num.toString().length > 12) return 'TOO BIG';
  
  if (num === 0) {
    return 0;
  }
  
  let counter = 0;
  // crete a results string ''
  let res = '';
  // We have strings representations   
  
  // while the number is > 0
  while (num > 0) {
    // the number is % 1000 not 0 
      // set out results sting equal to helper(current Num%1000) + counter a res
    if (num % 1000 !== 0) {
      res = `${getNums(num%1000)} ${thousands[counter]} ${res}`;
    }
      // num = num/1000 
  // counter++
    num = Math.floor(num / 1000);
    counter++;
  }
  
  return res;
}

const getNums = number => {
  // if the number is 0
    // return '';
  if (number === 0) {
    return '';
  } 
  else if (number < 20) {
    return upToTwenty[number];
  } 
  else if (number < 100) {
    return `${tens[Math.floor(number/10)]} ${getNums(number % 10)}`;
  } 
  else {
    return `${upToTwenty[Math.floor(number/100)]} Hundred ${getNums(number%100)}`;
  }
    // if the number is less than 20
     // return upToTwenty[number]
  // else if the number is < 100 
    // return floor this number tens[number/10] + getNums(number % 10)
  
  // This case should handle hundreds
  // return floor upToTwenty[num/100] + hundreds getnums(number%100)
}

let testNum = 1234 *5678 * 9000
let result = numToWords(testNum);
console.log(result);