smallestmissingposnum.js

function smallestMissingPositiveNumber(arr) {
  arr.sort((a, b) => a - b);
  let smallestPositive = 1;
  for (let i = 0; i < arr.length; i++) {
    if (arr[i] === smallestPositive) {
      smallestPositive++;
    } else if (arr[i] > smallestPositive) {
      return smallestPositive;
    }
  }
  return arr[arr.length - 1] + 1;
}

// TEST
const arr = [3, 4, -1, 1];
const smallestMissing = smallestMissingPositiveNumber(arr);
console.log(smallestMissing); // output: 2