I've just finished a JavaScript library to read zip file content. With it it's possible for example to get some zipped content with ajax, and use it in your webpage.

It works in all major browsers: firefox, chromium, opera, and ie7+ (althought it is quite slow in ie). Operations performed by zipfile are quite simple: ZipFile takes a string representing the file content. It extracts files headers as documented here. Decompression (the real work) is performed by deflate library. ZipFile has been heavily influenced by python zipfile module.

In Gecko 2.0, (future firefox 4.0), JavaScript typed arrays are available. They're supposed to be much more efficient than using strings for working with binary data. But I didn't use them: First, they're only available in a firefox nightly (probably soon in webkit trunk, but not yet). Then, when using them, useful string methods such as indexOf are not available.

You can see the online demo. It fetches and extracts the content of the library itself (I could not find a better example). Source code is available at github.