Insert missing whitespace in JS mode

(defun js-fix-spacing-line ()
  (interactive)
  (let ((current (char-after))
    (next (char-after 1))
    (old-point (point))
    (postfix)
    (difference 0))
    (labels
     ((incf-dif
       ()
       (when (< 0 (+ difference (- old-point (point))))
     (incf difference))
       (insert " "))
      (js-face
       (&optional (pos (point)))
       (get-char-property pos 'face)))
     (beginning-of-line)
     (while (not (eolp))
       (setf current (char-after (1- (point)))
         next (char-after))
       (cond
    ((or (char-equal current ?\ )
         (char-equal current ?\t)
         (char-equal next ?\ )
         (char-equal next ?\t)))
    ((and (equal (js-face (1- (point))) 'font-lock-string-face)
          (equal (js-face) 'font-lock-string-face)))
    ((and (equal (js-face (1- (point))) 'font-lock-comment-face)
          (equal (js-face) 'font-lock-comment-face)))
    ((and (equal (js-face (1- (point))) 'font-lock-keyword-face)
          (not (equal (js-face)
              'font-lock-keyword-face))
          (not (position current " \t")))
     (incf-dif))
    ((position next "=/|&%?><*^:}")
     (unless (and (position current "=!&|*+-^><") (not postfix))
       (setf postfix nil)
       (incf-dif)))
    ((position current "?:,{});,")
     (unless (char-equal next ?\;)
       (unless (and (char-equal current ?})
            (char-equal next ?\,))
         (unless (and (char-equal current ?\))
              (or (char-equal next ?\))
                  (char-equal next ?\.)
                  (char-equal next ?\[)))
           (incf-dif)))))
    ((char-equal current ?=)
     (unless (position next "=")
       (incf-dif)))
    ((position current "<>&|*/%^")
     (unless (and (char-equal next ?=)
              (and (char-equal current ?&)
               (char-equal next ?&))
              (and (char-equal current ?|)
               (char-equal next ?|)))
       (incf-dif)))
    ((position next "!~")
     (unless (position current "([")
       (incf-dif)))
    ((char-equal next ?+)
     (cond
      ((char-equal current ?+))
      ((looking-back "\\(\\sw\\|\\s_\\|\\]\\)\\s-*")
       (setf postfix t))
      (t (incf-dif))))
    ((char-equal next ?-)
     (cond
      ((char-equal current ?-))
      ((looking-back "\\(\\sw\\|\\s_\\|\\]\\)\\s-*")
       (setf postfix t))
      (t (incf-dif))))
    ((char-equal current ?+)
     (unless (position (char-before 1) "+;=/&%?><*:,{}[]")
         (unless (position next ")]}")
           (unless (looking-back "[=><?;/&%*,+|:]\\s-*+")
         (incf-dif)))))
    ((char-equal current ?-)
     (unless (position (char-before 1) "-;=/&%?><*:,{}[]")
         (unless (position next ")]}")
           (unless (looking-back "[=><?;/&%*,+|:]\\s-*-")
         (incf-dif))))))
       (forward-char)))
    (goto-char (+ old-point difference))))

(add-hook
 'js-mode-hook
 (lambda ()
   (local-set-key (kbd "C-x SPC") 'js-fix-spacing-line)))