A simple async PBKDF2 hashing library which I wrote based on the ideas behind StackOverflow's implementation. I haven't had the chance to test it yet, but it should be pretty close :)

hash.js

"use strict";

var crypto = require("crypto"),
    saltSize = 16,
    hashIterations = 5000;

function generateSalt(iterations, cb) {
    if (iterations === undefined) { iterations = hashIterations; }
    if (iterations < hashIterations) { throw new Error("iterations cannot be less than " + hashIterations); }

    var bytes = crypto.randomBytes(saltSize, function(err, buff) {
        if (err) { cb(err, null); }
        cb(null, iterations.toString(16) + "." + buff.toString("base64"));
    });
}

function hash(password, salt, cb) {
    var i = salt.indexOf(".");
    var iters = parseInt(salt.substring(0, i), 16);
    salt = salt.substring(i + 1);

    crypto.pbkdf2(password, salt, iters, 64, function(err, derivedKey) {
        if (err) { cb(err, null); }
        if (typeof derivedKey === 'string') {
            derivedKey = new Buffer(derivedKey, "binary");
        }

        cb(null, derivedKey.toString("base64"));
    });
}

module.exports = {
    generatePasswordHash: function(password, cb) {
        generateSalt(hashIterations, function(err, salt) {
            if (err) { cb(err, null); }
            hash(password, salt, function(err, result) {
                if (err) { cb(err, null); }
                cb(null, "$" + salt + "$" + result);
            });
        });
    },
    validatePasswordHash: function(password, hashed, cb) {
        var secondDollar = hashed.indexOf("$", 1);
        var salt = hashed.substring(1, secondDollar);

        hash(password, salt, function(err, result) {
            if (err) { cb(err, null); }
            cb(null, result === hashed.substring(secondDollar + 1));
        });
    }
};