visionmedia is his screen name, not the company where he works. He worked at a company called LearnBoost (https://www.learnboost.com/blog/welcome-aaron-and-tj/), which I can only assume is some sort of mob-style front for laundering JavaScript code. (Look at their employee list and GitHub repo)

Now, I've heard he works for Segement.io (in SOMA), but does so remotely.