plusOne.js

/*
Given a non-negative integer represented as a non-empty array of digits, plus one to the integer.
You may assume the integer do not contain any leading zero, except the number 0 itself.
The digits are stored such that the most significant digit is at the head of the list.
*/
/**
 * @param {number[]} digits
 * @return {number[]}
 */
 
const plusOne = function(digits) {
    for (let i = digits.length -1; i > -1; i--) {
        if (digits[i] === 9) {
            digits[i] = 0;
            if (i === 0) {
                digits.unshift(1);
                return digits;
            }
        } else {
            digits[i]++;
            return digits;
        }
    }
    return digits;
};