plovr: a Closure build tool

plovr is a build tool that dynamically recompiles JavaScript and Closure Template code. It is designed to simplify Closure development, and to make it more enjoyable.

The intended usage of plovr is as follows:

During development, you should be able to edit JavaScript and Soy files in your favorite text editor, refresh your web application in the browser, and have it load a newly compiled version of your code. Any errors or warnings resulting from compilation by the Closure Compiler should appear at the top of your web application so you can identify and fix them quickly.
During production, you should serve precompiled versions of your JavaScript that behave exactly as they did during development.

plovr displaying a Compiler warning inside the web page that loads the JavaScript code that contains the type checking warning.

In providing a build tool to assist in iterative JavaScript development, plovr also achieves the following:

Replaces the set of unrelated scripts that are usually required to build Closure code with a single JSON configuration file.
Exposes features of the Closure Compiler through the configuration file that were previously accessible only by writing Java code against the Compiler's API.
Facilitates the process of splitting JavaScript code into modules that can be downloaded separately, thereby reducing start-up time for web applications.

You can learn more about both Closure and plovr in Closure: The Definitive Guide (O'Reilly). Although it is not available in stores yet, it is possible to pre-order the book on Amazon (it is expected to be available in September 2010), or you can purchase the complete draft today via O'Reilly's Rough Cuts program.