If you're building your own NodeJS library and you like using Promises, chances are you'll want to implement your module API through promises.

NodeJscallbackPromise.js

// dual-module.js
var Q = require('q');

module.exports = {
    getFullName: function (firstName, lastName, callback) {
        var deferred = Q.defer();

        if (firstName && lastName) {
            var fullName = firstName + " " + lastName;
            deferred.resolve(fullName);
        }
        else {
            deferred.reject("First and last name must be passed.");
        }

        deferred.promise.nodeify(callback);
        return deferred.promise;
    }
}