Closure Compiler - Google Code

The Closure Compiler is a tool for making JavaScript download and run faster. It is a true compiler for JavaScript. Instead of compiling from a source language to machine code, it compiles from JavaScript to better JavaScript. It parses your JavaScript, analyzes it, removes dead code and rewrites and minimizes what's left. It also checks syntax, variable references, and types, and warns about common JavaScript pitfalls. To help you work with your transformed code, you can also install the Closure Inspector, a tool that makes it easy to use the Firebug JavaScript debugger with the Compiler's output. The Closure Compiler has also been integrated with Page Speed, which makes it easier to evaluate the performance gains you can get by using the compiler.

via code.google.com