http://code.google.com/p/closure-compiler/
http://stackoverflow.com/questions/28932/best-javascript-compressor
Closure Compiler
Closure Compiler is a JavaScript optimizing compiler. 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. It is used in many of Google's JavaScript apps, including Gmail, Google Web Search, Google Maps, and Google Docs.
Try it out!
It's easy to try the compiler through our web application at http://closure-compiler.appspot.com/
Get the Compiler
Download the compiler at http://closure-compiler.googlecode.com/files/compiler-latest.zip or using Maven.
The zip file contains a README with quick instructions to get you started.
User Documentation
You can read more about Closure Compiler at http://code.google.com/closure/compiler/.
We also have a few low-key wiki pages at http://code.google.com/p/closure-compiler/w/list. Please suggest new ones if you see anything missing.
Developer Documentation
The Closure Compiler javadocs are available at http://closure-compiler.googlecode.com/svn/trunk/javadoc/index.html
You can browse the source at http://code.google.com/p/closure-compiler/source/browse/#svn/trunk
We accept patches :)
