Sum big numbers

bigsum.js

function add(a, b) {

    // A queue to enqueue the result (minus the remainder)
    const queue = [];

    // Store the remainder
    let remainder = 0;

    // Determine the largest array length
    const maxLength = Math.max(a.length, b.length);
    for (let i = maxLength - 1; i >= 0; i--) {
        // +a[i] is a trick I picked up from another kata to convert to a number
        // Note: || checks if a value exists; otherwise, defaults to zero
        // i - maxLength + a.length is basically saying index value minus max length plus actual length e.g. (5 - 10) = -5 + 8 = 3
        // (index 3 of first array)
        const sum = (+a[i - maxLength + a.length] || 0) + (+b[i - maxLength + b.length] || 0) + remainder;
        const value = (sum % 10);
        remainder = (sum - value) / 10; // 25 - 5 / 10 = 2, so the remainder is 2

        // Add to the queue e.g. remove 2 from 23 to give just 3
        queue.unshift(value);
    }

    // Add any remainder to the queue
    if (remainder > 0 && remainder < 10) {
        queue.unshift(remainder);
    }

    // Join the queue and remove leading zeros
    return queue.join('').replace(/(?:^0*)/, '');

}

console.log(add('1234567890', '1234567890'));