Take two sorted lists of numbers and merge them into a single sorted list

sort-merge.js

var list1 = [2, 4, 5, 6];
var list2 = [3, 5, 8, 9];
merged_list = merge_sorted_list(list1, list2);
alert(merged_list);

function merge_sorted_list(list1, list2) {
  merged_list = list1.concat(list2);
  return merged_list.sort(numsort);
}

function numsort(a, b) {
  return a - b;
}