JS-AES is a JavaScript implementation of the Advanced Encryption Standard using Counter Mode.
The best way to understand the aes.js source code is to follow along with a FIPS 197, which you can download from http://csrc.nist.gov/publications/fips/fips197/fips-197.pdf
After you include the aes.js file into your page, you can interact with it in the following manner:
Create two new crypto objects
var aSide = new AES.Crypto(AES.generateKey());
var bSide = new AES.Crypto(aSide.key);
Sync the two cryptos
bSide.setCounter(aSide.getCounter());
Encryption
var cipherText = aSide.encrypt("the quick brown fox jumped over the lazy dog");
Decryption
var plainText = bSide.decrypt(cipherText);
Compare
plainText == "the quick brown fox jumped over the lazy dog";
If you have any questions, comments or just want to talk shop about crypto, feel free to reach me through my website at http://www.robertsosinski.com.