My solution to codewars "Next bigger number with the same digits" kata

next-biggest.js

// write array `a` onto array `b` starting at position `p`
function overlay(a, b, p) {
    for (let [i, n] of a.entries()) {
        b[p+i] = n;
    }
    return b;
}

// in an array, swap items at indexes i1 and i2
function swap(arr, i1, i2) {
    const [a, b] = [arr[i1], arr[i2]];
    arr[i1] = b;
    arr[i2] = a;
}

/**
 * Algorithm:
 *
 *  - move from right to left, one digit (d) at a time
 *  - for each digit (d), compare it to the digits that follow it (again moving from right to left)
 *  - if any following digit (f) is found that is greater than (d), swap their positions and break out of all loops
 *  - sort all the digits that come after (f) (which is now in (d)'s original position)
 *  - done!
 */

function nextBigger(n){
    let digits = n.toString().split('');

    for_each_digit:
    for (let i = digits.length - 1; i >= 0; --i) {

        let d = digits[i];
        let lower;

        for_each_trailing_digit:
        for (let j = digits.length - 1; j > i; --j) {

            if (d < digits[j]) {
                swap(digits, i, j);
                let trailing = digits.slice(i + 1, digits.length);
                trailing.sort();
                overlay(trailing, digits, i + 1);
                break for_each_digit;
            }

        }

    }

    let answer = +digits.join('');

    return n == answer ? -1 : answer;
}