Facebook's React library allows you to construct composable, reusable UI components with ease. Dustin Getz and Daniel Miladinov from Wingspan Technology gave a great demo departing form the ubiquitous ToDo app by leveraging underscore's functional tools against React's immutable state and virtual dom. It was cool to see how both the state and the functions that update it can be created and passed down dynamically as the components are rendered. I really like this library and the talk showed how to use it in an even more concise and declarative fashion.