Summ strings

str_summ.js

function summ_char (str1, str2) {
  return '' + (parseInt(str1) + parseInt(str2));
}

function summ (str1, str2) {
  var num1 = str1.split('');
  var num2 = str2.split('');
    
  var tmp1, tmp2;
  var result = '';
  var mem = 0;
  var nextStep = true;
  while (nextStep) {
    if (num1.length) {
      tmp1 = num1.pop(); 
    } else {
      tmp1 = 0;
    }
    if (num2.length) {
      tmp2 = num2.pop(); 
    } else {
      tmp2 = 0;
    }
    if (mem > 0) {
      tmp1 = summ_char(mem, tmp1);
      mem = 0;
    }
    var res = summ_char(tmp1, tmp2);
    if (res.length > 1) {
      mem = 1;
      res = res.split('').pop();
    }
    if (num1.length <= 0 && num2.length <= 0) {
      nextStep = false;
    }
    result = res + result;
  }

  return result;
}


console.log(summ('1112', '190'))