0989-add-to-array-form-of-integer.js

/**
 * @param {number[]} num
 * @param {number} k
 * @return {number[]}
 */
var addToArrayForm = function (num, k) {
    num.reverse();
    let i = 0;

    while (k > 0) {
        const digit = k % 10;
        i < num.length ? (num[i] += digit) : num.push(digit);

        const carry = Math.floor(num[i] / 10);
        num[i] %= 10;

        k = Math.floor(k / 10);
        k += carry;
        i++;
    }

    return num.reverse();
};