实现非负大整数相加

function sumBigNumber(a, b) {
  let res = '';
  let temp = 0;
  
  a = a.split('');
  b = b.split('');
  
  while (a.length || b.length || temp) {
    temp += ~~a.pop() + ~~b.pop();
    res = (temp % 10) + res;
    temp  = temp > 9
  }
  return res.replace(/^0+/, '');
}