Every Node.js programmer must know about Promises. When we are dealing with large application where multiple queries are made to database and multiple parallel tasks are done, promises come in handy. They break you out from nested call backs aka callback hell. Bluebird (https://github.com/petkaantonov/bluebird
) an excellent library with loads of features for implementing Promises. One feature I really like is promisify it converts existing function into promise. A very very useful library checkout yourself.