Byte compile emacs packages

what is it

It was useful for me when I was installing 28 emacs on ubuntu and then lost syntax highlighting in js2 mode. I then found this fix. did M-: and wrote this to fix it:

;; dont forget the exact file path
(byte-recompile-directory (expand-file-name "~/.emacs.d/elpa/js2-mode-20130307.2012/") 0 t)