bluebird-promisify.js

const bluebird = require('bluebird');

function echo(text, callback) {
  callback(null, text);
}

const echoPromise = bluebird.promisify(echo);

echo('Hello', (err, result) => {
  console.log(`From callback: ${result}`);
});

echoPromise('Hello').then((result) => {
  console.log(`From promise: ${result}`);
});