While it doesn't enforce the guidelines, their Closure Compiler enforces the variable types and encapsulations declared in the JSDoc comments with warnings. http://code.google.com/closure/compiler/

On another note, a Google engineer argues against Crockford's arguments for functional inheritance while pitching the benefits of the Closure Compiler and Library: http://www.bolinfest.com/javascript/inheritance.php I find his points are well made.