Example of function with callback that returns a promise. Can use both promise chaining and callback.

test-promisify.js

'use strict';

var q = require('q');

function promisifyme(value, callback) {
	var deferred = q.defer();

	if (value === 3) {
		deferred.resolve(123);
	}

	if (value === 5) {
		deferred.reject(new Error("321"));
	}
	
	deferred.resolve(333);

	deferred.promise.nodeify(callback);

	return deferred.promise;
};


promisifyme(3).then(function (result) {
	console.log('he promised me first and he did it!');
}).catch(function (err) {
	console.log('he promised me first, but something wrong happened and he brought me ' + err);
});

promisifyme(5).then(function (result) {
	console.log('he promised me first and he did it!');
}).catch(function (err) {
	console.log('he promised me first, but something wrong happened and he brought me ' + err);
});

promisifyme(3, function (err, result) {
	if (err) {
		return console.log('He called the callback with an error!');
	}

	console.log('He called the callback with the result of ' + result);
});

promisifyme(5, function (err, result) {
	if (err) {
		return console.log('He called the callback with ' + err);
	}

	console.log('He called the callback with the result of ' + result);
});