JS String Incrementer

string-incrementer.js

/*
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

Attention: If the number has leading zeros the amount of digits should be considered.
*/

function incrementString(input) {
  if(isNaN(parseInt(input[input.length - 1]))) return input + '1';
  return input.replace(/(0*)([0-9]+$)/, function(match, p1, p2) {
    var up = parseInt(p2) + 1;
    return up.toString().length > p2.length ? p1.slice(0, -1) + up : p1 + up;
  });
}

console.log(incrementString("foo"));//should log foo1
console.log(incrementString("foobar23"));//should log foobar24
console.log(incrementString("foo0042"));//should log foo0043