Pure javascript implementation of ChaCha20 originally written by @devi supporting draft-irtf-cfrg-chacha20-poly1305-01.
Being packaged here as a simple node.js and browserify module.
var chacha20 = require("chacha20");
var key = new Buffer(32);
key.fill(0);
var nonce = new Buffer(8);
nonce.fill(0);
var plaintext = "testing";
// pass in buffers, returns a buffer
var ciphertext = chacha20.encrypt(key, nonce, new Buffer(plaintext));
console.log(ciphertext.toString("hex")); // prints "02dd93d9c99f5a"
console.log(chacha20.decrypt(key, nonce, ciphertext).toString()); // prints "testing"
The handling of the nonce differs between the reference and IETF Draft, where the reference uses an 8-byte nonce and the draft uses a 12-byte one with the first 4 bytes being a sender unique identifier. Passing a difference nonce buffer size will choose either mode.