Code Wars: String incrementer

https://www.codewars.com/kata/54a91a4883a7de5d7800009c/train/javascript

Your job is to write a function which increments a string, to create a new string. If the string already ends with a number, the number should be incremented by 1. If the string does not end with a number the number 1 should be appended to the new string.
Examples:
foo -> foo1
foobar23 -> foobar24
foo0042 -> foo0043
foo9 -> foo10
foo099 -> foo100
Attention: If the number has leading zeros the amount of digits should be considered.

My Solution: 

function incrementString (strng) {
  let regex = /[0-9]/g;
  let index = strng.search(regex);
  let arr = [];
  
  //split string at where a number first appears
  if (index === -1 || strng === "") {
    return strng + "1";
  }
  else arr.push( strng.substring(0, index), strng.substring(index, strng.length) );
  
  //loop through element of array with numbers and increment by 1 when necessary
  let secondArr = arr[1].split("");
  for (let i = secondArr.length - 1; i >= 0; i--) {
    if (secondArr[i] < 9) {
      secondArr[i]++;
      break;
    }
    else if (i === 0 && secondArr[i] == 9) {
      secondArr[i] = 10;
    }
    else if (secondArr[i] == 9) {
      secondArr[i] = 0;
    }
  }
  secondArr = secondArr.join("");
  return arr[0] + secondArr;
}

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