The developers of GWT have often referred to it as a "necessarily leaky abstraction." Why is that a good thing? It means that GWT isn't a walled garden of functionality. Using the JavaScript Native Interface (JSNI), you can easily implement Java methods using handwritten JavaScript, making it possible to produce and consume pure JavaScript libraries even while using your favorite Java tools. Best of all, the GWT compiler actually optimizes your handwritten JavaScript! Learn from GWT compiler guru Scott Blum how JSNI works and how you can take advantage of it.