Download the .deb package below according to your SO's architecture: 32 bit = i386, 64 bit = amd64.
Install with GDebi Package Installer or enter the following command in a Terminal (in the folder where is the downloaded file):
For 32 bit: sudo dpkg -i nodejs-unofficial-stable_8.0.0_i386.deb
For 64 bit: sudo dpkg -i nodejs-unofficial-stable_8.0.0_amd64.deb