Merge two objects/arrays upto any depth, written in coffeescript

merge.coffee

merge = (left, right) ->
  return left unless (typeof left is typeof right is 'object') and right isnt null
  return left unless (Array.isArray left) is (Array.isArray right)
  ret = if Array.isArray left then [] else {}
  for key, value of left
    ret[key] = left[key]
  for own key, value of right
    if key of ret
      ret[key] = merge ret[key], right[key]
    else
      ret[key] = right[key]
  return ret