Chris Veness has written a JavaScript implementation of AES in counter operation mode some time ago. I wrapped the code up into a class for easier use.
Download it here: aes.class.js (18.25 KiB, 62 downloads)
var text = 'Hello, world!'; var password = 'itsmysecret'; var blocksize = 256; // can be 128, 192 or 256 var crypted = AES.encrypt( text, password, blocksize ); // do something... var decrypted = AES.decrypt( crypted, password, blocksize );