Setting Emacs' js2-mode indent level on the fly. See refs @ http://www.xradiograph.com/JavaScript/Emacs

js2-indent-set.el

;;; do I even need to say how preliminary all of this is?

;;; in-progress variant to use universal-argument or param
(defun js2-cust-idnt (&optional indt)
  "set indentation in this buffer"
  (interactive)
  ;; TODO if no prefix-arg and no idnt, prompt for indent?
  (let ((indent-level (if indt indt
                      current-prefix-arg)))
       (setq js2-basic-offset indent-level)))

;; sample

(defun js2-idnt-3 ()
  (interactive)
  (js2-cust-idnt 3))
  

;;; older functions
(defun js2-indent-custom (position)
  "set indentation in this buffer"
  (interactive)
  (setq js2-basic-offset position))
  
(defun js2-indent-2 ()
  "set indentation to 2 in this buffer"
  (interactive)
  (js2-indent-custom 2))

(defun js2-indent-4 ()
  "set indentation to 2 in this buffer"
  (interactive)
  (js2-indent-custom 4))