A browser's JavaScript engine can seem like a magical black box. During this session, we'll show you how they work from 10,000 feet and give you the tricks to compile all the popular engines out there including JavaScriptCore, V8, and SpiderMonkey). We'll inspect the internals of the engine, and debug+profile your favorite code snippets. Armed with just a little extra knowledge about this black box, you will be ready to take a new look at JavaScript apps.