Emacs-lisp command for compiling a javascript file into a bookmarklet, by stripping unnecessary characters and adding a wrapper.

myjs-compile-bookmarklet.el

;;; myjs-compile-bookmarklet.el --- strip javascript code as bookmarklet  -*- lexical-binding: t; coding: utf-8; lisp-indent-offset: nil; -*-

;; Copyright (C) 2018  Klaus-Dieter Bauer

;; Author: Klaus-Dieter Bauer <kdb.devel@gmail.com>
;; Keywords: javascript, bookmarklet

;; This program is free software; you can redistribute it and/or modify
;; it under the terms of the GNU General Public License as published by
;; the Free Software Foundation, either version 3 of the License, or
;; (at your option) any later version.

;; This program is distributed in the hope that it will be useful,
;; but WITHOUT ANY WARRANTY; without even the implied warranty of
;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
;; GNU General Public License for more details.

;; You should have received a copy of the GNU General Public License
;; along with this program.  If not, see <http://www.gnu.org/licenses/>.

;;; Commentary:

;; See docstrings.
;; 
;; Published as https://gist.github.com/kbauer/68db9deb88ae170a8f18a2b84de74fb6

;;; Code:

(defconst myjs-compile-bookmarklet-metachars 
  "(){}[];+-*/.,%>=<!\"'`|&"
  "A string of operator-only characters. 
Used for stripping unneeded whitespace between operators and identifiers.")

(defun myjs-compile-bookmarklet ()
  "Copy current buffer as bookmarklet.

In detail this means putting a copy of `buffer-string' 
into `buffer-file-name'.txt and the (clipboard), where

  - Comments and syntactically irrelevant whitespace are
    stripped, to reduce character count and to reduce the code
    to a single-line string.
  
  - A wrapper is added, that contains the file name as a comment,
    the `javascript:' prefix, required for executing javascript from
    bookmarks, and a wrapper-function, that prevents the bookmarklet
    from cluttering the namespace of the function.

==== KNOWN ISSUES ====

  - Some whitespace may be incorrectly judged as syntactically irrelevant,
    e.g. whitespace in string-literals. Workaround: Avoid such strings,
    its only a bookmarklet after all."

  (interactive)
  (when (buffer-file-name)
    (save-buffer))
  (let ((raw-string (buffer-string))
        (file-name (buffer-file-name)))
    (with-temp-buffer
      (insert raw-string)
      (goto-char (point-min))
      (save-excursion
        (while (search-forward-regexp (rx "/*" (*? anything) "*/") nil t)
          (replace-match "")))
      (save-excursion
        (while (re-search-forward "//.*" nil t)
          (replace-match " ")))
      (save-excursion
        (while (re-search-forward "[[:blank:]\n]+" nil t)
          (unless (eq (save-excursion (forward-char -1) (face-at-point))
                    'font-lock-string-face)
            (replace-match " "))))
      ;; Removal of whitespace separating punctuation outside strings.
      (save-excursion
        (while (search-forward-regexp " " nil t)
          (let ((a (char-after (point)))
                (b (char-before (- (point) 1)))
                (meta (append myjs-compile-bookmarklet-metachars nil)))
            (when (and (or (memq a meta) (memq b meta))
                       (not (eq (save-excursion (forward-char -1) (face-at-point))
                              'font-lock-string-face)))
              (delete-char -1)))))

      ;; Add "private namespace" and "javascript:" wrappers.
      (insert 
        "javascript:"
        (if file-name
            (concat "/* " (file-name-nondirectory file-name) " */")
          "")
        "(function(){")
      (goto-char (point-max))
      (while (memq (char-before) '(?\  ?\n ?\t))
        (backward-delete-char 1))
      (insert "})();undefined;")

      ;; Export to .txt file.
      (when file-name
        (let ((txt-file-name (concat file-name ".txt"))
              (contents (buffer-string)))
          (with-temp-buffer
            (when (file-exists-p txt-file-name)
              (insert-file-contents txt-file-name))
            (if (string= contents (buffer-string))
                (message "%s: Unchanged contents, not updated." txt-file-name)
              (erase-buffer)
              (insert contents)
              (write-file txt-file-name)))
          (message "Exported bookmarklet to `%s'" txt-file-name)))

      ;; Copy to kill-ring
      (message "Copied bookmarklet to kill-ring (%d characters)" (point-max))
      (kill-region (point-min) (point-max))
      
      ;; Display result
      (with-selected-window (display-buffer (get-buffer-create "*myjs:bookmarklet*"))
        (erase-buffer)
        (yank)
        (insert "\n\n"
          (format "Copied bookmarklet to kill-ring (%d characters)" (point-max)))
        (unless (eq major-mode 'js-mode)
          (js-mode)))))
  nil)



(provide 'myjs-compile-bookmarklet)
;;; myjs-compile-bookmarklet.el ends here