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Considering that you already have rootfs write access and and have switched on your chromebook to dev mode, it is possible to install NodeJS dev env on chromebook (keeping your OS to ChromeOS. This article is not about ChrUbuntu)

If you need help with dev mode and rootfs write access, consider following Chromium OS poking around article.

Download xz package and nodejs package from ArchLinux - 
xz - http://www.archlinux.org/packages/core/i686/xz/
node - https://www.archlinux.org/packages/community/i686/nodejs/
There is a little ‘Download from mirror’ link on the page. If you don’t find, just Find on Page for word ‘download’. Both these downloaded packages should be in your Downloads folder that opens up when you open Chrome OS files app.
switch to terminal (Ctrl+Alt+T) will open terminal as one of the browser tabs.
type SHELL and hit enter as follows, and proceed

CHRONOS> SHELL 

$ sudo su , enter (switch to root)
$ pwd, enter (it should display only / )
$ cd /home/chronos/user/Downloads/
$ tar -xvf xz*.tar.xz
$ cd /usr/bin
$ cp * /usr/bin
$ cd ..
$ cd .. (doing it twice will bring you back to Downloads directory)
$ xz -d node*.tar.xz
$ tar -xvf node*.tar
$ cd /usr/bin
$ cp * /usr/bin
$ cd ..
$ cd ..
$ node -v (should display you the installed node version)
$ curl https://npmjs.org/install.sh (download this file to same Downloads folder)
$ sh install.sh (will install npm)
$ npm version (should display npm version, might be outdated)
$ npm update npm -g (npm can update itself)
$ npm version (should be latest now)
AND JOY!