You may want to take a look at the Stanford JS Crypto Library
GitHub
Website with Examples
From the website:
SJCL is secure. It uses the industry-standard AES algorithm at 128, 192 or 256 bits; the SHA256 hash function; the HMAC authentication code; the PBKDF2 password strengthener; and the CCM and OCB authenticated-encryption modes.
SJCL has a test page that shows how long it will take.
184 milliseconds for a SHA256 iterative. And 50 milliseconds for a SHA-256 from catameringue.
Test page
Sample code:
Encrypt data:
sjcl.encrypt("password", "data")
Decrypt data: sjcl.decrypt("password", "encrypted-data")