TernopilJS. Lesson 2. Task 1. Good solution

next-bigger.js

function nextBigger(number) {
  var digits = number.toString().split('').map(function(item) {
    return parseInt(item, 10);
  });

  function swap(arr, firstIndex, secondIndex) {
    var resultArr = arr.slice(0);
    resultArr[secondIndex] = arr[firstIndex];
    resultArr[firstIndex] = arr[secondIndex];
    return resultArr;
  }

  function replaceDigits(arr, lastIndex) {
    for (var i = lastIndex; i >= lastIndex - 1; --i) {
      var start, end;
      if (arr[i] < arr[lastIndex]) {
        if (arr[i] === 0) {
          start = arr.slice(0, i);
          // first value is smallest non zero, second - zero
          end = swap(arr.slice(i, arr.length).sort(), 0, 1);
        } else {
          arr = swap(arr, i, lastIndex);
          start = arr.slice(0, lastIndex);
          end = arr.slice(lastIndex, arr.length).sort();
        }

        return start.concat(end);
      }
      if (i - 1 === 0 && arr[0] < arr[lastIndex]) {
        arr = swap(arr, 0, lastIndex);
        start = arr.slice(0, i);
        end = arr.slice(i, arr.length).sort();

        return start.concat(end);
      }
    }

    return replaceDigits(arr, --lastIndex);
  }

  return parseInt(replaceDigits(digits, digits.length - 1).join(''), 10);
}