Array nested sum - recursion

// 3. Sum all numbers in an array containing nested arrays.
// arraySum([1,[2,3],[[4]],5]); // 15
var arraySum = function(array) {
  var result = 0;
  if(! Array.isArray(array)) {
    return array;
  } else {
    array.forEach(arr => {
      result += arraySum(arr);
    })
  }
 return result;
};
console.log(arraySum([1,[2,3],[[4]],5]));