I know you'll find this hard to believe dear reader but I'm a big fan of using Emacs to write JavaScript. One thing that irked me in the past is that none of the libraries got the indentation and other formatting how I wanted. Luckily, I recently stumbled onto js-beautify (via the most excellent jsFiddle.

Lo and behold, there is a command line interface to beautifying JavaScript! Good thing Emacs can call shell commands on text so easily. Thus, we have:

;;; js-beautify.el -- beautify some js code

(defgroup js-beautify nil
  "Use jsbeautify to beautify some js"
  :group 'editing)

(defcustom js-beautify-args "--jslint-happy --brace-style=end-expand
  "Arguments to pass to jsbeautify script"
  :type '(string)
  :group 'js-beautify)

(defcustom js-beautify-path "~/projects/js-beautify/python/jsbeautifier.py"
  "Path to jsbeautifier python file"
  :type '(string)
  :group 'js-beautify)

(defun js-beautify ()
  "Beautify a region of javascript using the code from jsbeautify.org"
  (let ((orig-point (point)))
    (unless (mark)
    (shell-command-on-region (point)
                             (concat "python "
                                     " --stdin "
                             nil t)
    (goto-char orig-point)))

(provide 'js-beautify)
;;; js-beautify.el ends here

I like it so much I have bound to M-t (for tidy) in a mode hook:

(local-set-key "\M-t" 'js-beautify)

If you want to follow any updates, I've put this snippet up as a Gist on GitHub so feel free to clone and send me any pull requests.