50js2-mode.el

(require 'js2-mode)
(add-hook 'js2-mode-hook 'ac-js2-mode)

(defun js2-mode-hooks ()
  (font-lock-add-keywords nil
                          '(("^[^\n]\\{80\\}\\(.*\\)$" 1 font-lock-warning-face t)))

  (defun underscore-require ()
    (interactive)
    (insert (format "var _ = require('underscore');"))
    )
  (local-set-key (kbd "C-x c j") 'underscore-require)
  )

(add-hook 'js2-mode-hook 'js2-mode-hooks)

(custom-set-variables
 '(js2-basic-offset 2)
 )

(add-to-list 'auto-mode-alist '("\\.js$" . js2-mode))