script.js

//sum array of two numbers and all numbers in between
//positive numbers only
function sumAll(arr) {
  var min = arr.reduce(function(a, b) {
    return Math.min(a, b);
  });
  var max = arr.reduce(function(a, b) {
    return Math.max(a, b);
  });
  if (min == max) {
    return min*2;
  }
  if (min < 0) {
    return "abort";
  }
  return sumNums(min);
  
  function sumNums(x) {
   if(x == max) {
      return max;
   }
   return x + sumNums(x + 1);
  }
}

sumAll([5, 10]);