Javascript MD5 singleton

I really love how Yahoo! are spreading the gospel on sound javascript code practices and design patterns, popularizing good ideas among the masses, the most recent example being the module pattern.

In some ways it's the pop version of Douglas Crockford's writings on javascript, in this case private members in javascript, which tells the story of how almost any higher aspect of programming in javascript is accomplished through exploiting the few properties of the function keyword and closures. You can do most kinds of programming in javascript, there is just very rarely any syntactic aid for it.

By contrast, posts like this one would be the boring narrative recount telling you to read the gospel. I'm actually going to add a tiny bit more than that, though, and give an example of how to (re)structure code (not even necessarily your own) to use the module pattern, where it did not use to. It greatly helps keeping mess out of your way.

For a one-off hack (a user script that shows bookmark permalinks at del.icio.us, so you can share them with others, even before more people than yourself have bookmarked the url), I needed a javascript MD5 implementation. Paul Johnston's one (linked) is BSD licensed and works well, but exposes lots of namespace clutter, so I wrapped it up in an MD5 object, exposing only the bits I wanted from it.

Basically, I ended up framing the code inside a var MD5 = (function(){ /* original function definitions here */ return {hash:hex_md5}; })(); block, which exposes the only method I wanted as MD5.hash( data ). No namespace pollution, readable code.

Since an MD5 component is something I often want to use to interface with the world (here it was just to interface with Del.icio.us, which uses hex encoded MD5 hashes of urls for permalinks), I decided to go on and wrap up a version exposing the full (MD5 related) feature set of the lib, though, into a tidy MD5 module.

The API is very lightly wrapped, into methods MD5.string(data), which does a raw MD5 hash on its input string, MD5.hex(data), returning the same, but hexified, MD5.base64(data), ditto but base64 encoded instead, and the same method names with an "MD5.hmac." prefix for the hmac variants. (There is an MD5.test() method for good measure too.) The same config options as the original are supported too, and with the same default values, so set MD5.b64pad = "=" for real base64.

I thought I'd mention this too, here: if you want a similar javascript AES/Rijndael singleton, you should peek at Josh Davis's project on javascript cryptography, which has embarked on a similar path to the above since its conception. It might still be applying an UTF-8 codec on all data that passes through it, but if you need raw AES, just drop the few utf8 related lines, and you've got one.