Sometimes, undefined is not a function. As mortal programmers, we ship bugs to production everyday. Bugs slow us down, frustrate our users, and cause us to have crises of confidence. Don't go alone–type systems in TypeScript, Flow, and GraphQL can improve your confidence and help you ship less bugs. We'll start with why: a practical look at what you'll get from embracing types. Then, a gentle introduction to the ideas behind them. Finally, we'll explore the possibilities of a type system over the network.