sum-big-numbers.js

function SumBigNumbers  (a, b) {
  var res = '', c = 0;
  a = a.split('');
  b = b.split('');
  while (a.length || b.length || c) {
    c += ~~a.pop() + ~~b.pop();
    res = c % 10 + res;
    c = c > 9;
  }
  return res;
}

// const SumBigNumbers = (a, b) => {
//   a = a.replace(/^0+/, '').split``.reverse``;
//   b = b.replace(/^0+/, '').split``.reverse``;
//   const max = Math.max(a.length, b.length);

//   let result = [];
//   for (let memo = 0, i = 0; i < max; i++) {
//     let res = parseInt(a[i] || 0) + parseInt(b[i] || 0) + memo;
//     result[i] = res % 10;
//     memo = (res - result[i]) / 10;
//     if (memo) result.push(memo);
//   }

//   return result.reverse().join``;
// }