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.

Virtual Machine For Browser

Strongly Typed Javascript:Generator

Silksmith

Forbidden Functions is a static JavaScript analyser which warns you about functions you don't want to allow.

Dust JS Closure

Silksmith

This plugin minifies CSS and JavaScript either embedded in or reference by HTML files.