If you look at the source of Google pages with JavaScript, you’ll find that the JavaScript is clearly not readable — or maintainable. For example, all variables and functions are one-letter named (at least, the first 26 are…); there are no extraneous white-spaces or linebreaks; there are no comments; and so on.
The benefits of this compiler are clear: pages load faster, JavaScript execution is faster, and as a bonus, competitors will have a hard time understanding your obfuscated code.
Clearly, Google is using some sort of a JavaScript-to-JavaScript compacting compiler. I am wondering if what they’re using is an in-house tool? If not, what are they using? Are there any publicly available (ideally, free/open-source) tools of that sort?
YUI Compressor is a Java app that will compact and obfuscate your Javascript code. It is a Java app that you run from the command line (and would probably be part of a build process).
Another one is PHP Minify, which does a similar thing.