function nextBigger(n){
  // helper function to turn numbers into array of digits
  function getDigits(number) {
    const digitsArr = [];
    while(number >= 1) {
      digitsArr.push(Math.floor(number % 10));
      number /= 10;
    }
    return digitsArr;
  }
  
  // store digits in the correct order
  const digits = getDigits(n).reverse();
  // store length
  const length = getDigits(n).length;
  // sort the digit array to find biggest possible number
  const largestNum = +[...digits].sort((a,b) => b - a).join("");
  // if input is already biggest, return
  if (n === largestNum) return -1;
  
  // actual function to help find the next biggest number
  function findSubNextBigger(arr) {
    const number = +arr.join("")
    const length = arr.length;
    const largestNum = +[...arr].sort((a,b) => b - a).join("");
    if (number === largestNum) return -1;
    let index;
    // loop through each numbers and find indices of the two numbers
    // to be swapped
    outer: for(let i = 0; i < length; i++) {
      for(let j = i; j < length - 1; j++) {
        if (arr[length - 1 - i] > arr[length - 2 - j]) {
          let curDigit = arr.splice(length - 1 - i, 1)[0];
          arr.splice(length - 2 - j, 0, curDigit);
          index = length - 2 - j;
          break outer;
        } 
      }
    } 
    // truncate the arr from where the indices were swapped
    // and find lowest possible combination with the remaining digits
    const lowestArr = arr.slice(index + 1).sort((a, b) => a - b);
      arr.splice(index + 1, length, ...lowestArr);
    return arr;
  }
  
  // starting from the end, evaluate the sub arr  to find the next biggest number
  for (let i = length - 1; i >= 0; i--) {
    if(findSubNextBigger(digits.slice(i)) !== -1) {
      // truncate the sub array from the digits array and join the return from 
      // findSubNextBigger function
      digits.splice(i, length, ...findSubNextBigger(digits.slice(i)));
      break; // exit loop as new biggest is found
    };
  }
  
  // join the array back and return
  return +digits.join("") || -1;
}