code: function(arr, num) {
      if (isUndefined(num)) return arr[arr.length - 1];
      var start = arr.length - num < 0 ? 0 : arr.length - num;
      return arr.slice(start);
    }
docs: *
  @method last([num] = 1)
  @returns Mixed
  @short Returns the last element(s) in the array.
  @extra When `num` is passed, returns the last `num` elements in the array.
  
  @example
  
  [1,2,3].last()  -> 3
  [1,2,3].last(2) -> [2,3]
  
  @param {number} [num]
  
  *