In 2012 and 2013, Facebook did something unprecedented: designed a new statically-typed programming language, and then converted its entire web frontend to begin using it – without needing to rewrite the tens of millions of lines of code that run www.facebook.com. This talk will give a brief introduction to the Hack language, and then discuss in depth both the technical aspects of converting Facebook’s code and the social aspects of rallying an entire engineering organization behind that transition.

Josh Watzman is a software engineer at Facebook, joining right after completing CMU’s undergraduate CS program. After working in Facebook’s frontend on news feed, he felt the pain of working in a completely untyped language, and joined the Hack team in order to help the conversion effort. With the conversion at Facebook largely complete, he’s involved in the open-source side of Hack, and loves bringing the joy of the language to as many people as possible.