As of iojs 2.0.2, Homebrew ships with its own formula for iojs. This isn't preferrable, in my opinion, since global npm packages aren't being ran properly.
If you'd like to use this anyway, simply doing brew install iojs is not enough. To get iojs working on Homebrew You will need to unlink node first then use link --force to install iojs.
You have just read Installing iojs on Homebrew, written on May 19, 2015. This is Today I Learned, a collection of random tidbits I've learned through my day-to-day web development work. I'm Rico Sta. Cruz, @rstacruz on GitHub (and Twitter!).