installing io.js is now really easy thanks to the io.js and nvm team. They provides prebuilt binaries for arm.
io.js require packages that are not available on the standard (Wheezy) need to change to Jessie. Update your package url
$ sudo nano /etc/apt/sources.list
in the opened file comment the Wheezy package line and add
deb http://mirrordirector.raspbian.org/raspbian/ jessie main contrib non-free rpi
Now you need to do a full upgrade
$ sudo apt-get update && apt-get upgrade && apt-get autoremove
if you have already nvm installed, please be sure to use the latest version (min v0.23.0, nvm --version). two install options are available :
curl script
curl -o- https://raw.githubusercontent.com/creationix/nvm/v0.25.4/install.sh | bash
or make a regular installation following nvm's instructions
$ nvm install iojs
will download binaries for io.js and npm and symlink them to node and npm command.
Go play with es6 !