recursion_addition.js

var arraySum = function(array) {
  var total = 0;
  if(array.length === 0) {
    return 0;
  } 
  var popped = array.pop();
  if(Array.isArray(popped)) {
    total += arraySum(popped);
    return total += arraySum(array);
  } 
  return total += popped + arraySum(array);
};