Do you want to show your caring for the JavaScript community by doing some sharing? At work, are you thinking that the code you keep pasting in project after project should become an internal library? The key to creating a great library is designing an API that people love using. We will walk through API design patterns in popular JavaScript libraries, including LoDash, Q, Moment, and Request. You will learn what patterns work, what mistakes have been made, and how to apply this knowledge to your own JavaScript libraries and tools.