Write a function accepts numbers as strings and adds them. Return them as strings.

math.js

function validateInput(a) {
  var valid = a >= 0 ? a : false;
  return valid;
}

function doIt(a, b) {
  
  var arr = [],
      i = 0,
      x = parseInt(a, 10),
      y = parseInt(b, 10),
      sum = 0;
  
  arr.push(x);
  arr.push(y);

  for(i; i<=arr.length; i++) {
    if (validateInput(arr[i])) {
      sum += arr[i];
    }
  }
  console.log(sum.toString());
}

doIt('89234025487252189', '20342034982340220341');