After tryng different solutions, this one works for me.
Remember: never use SUDO, like I did the first time and like is written elsewhere 😉
echo 'export PATH=$HOME/local/bin:$PATH' >> ~/.bashrc
curl http://nodejs.org/dist/node-latest.tar.gz | tar xz --strip-components=1
make install # ok, fine, this step probably takes more than 30 seconds...
curl https://www.npmjs.org/install.sh | sh
npm install -g grunt