There are a few ways of installing nodejs on debian. You can build from source or you can use the backports repository.
I personally use the repository as then the system package manager can handle updating etc. I normally find packages on servers that are built from source often get left and never get updated. Also if you are using a vps or limited machine you don’t have to strain the system with compiling.
add-apt-repository 'deb http://ftp.us.debian.org/debian wheezy-backports main' apt-get update apt-get install nodejs-legacy
cd /tmp wget https://www.npmjs.org/install.sh --no-check-certificate chmod +x install.sh ./install.sh