An example of async programming with bluebird-promisell - Get Tweets by UserId

getTweetsByUserId.js

var P = require('bluebird-promisell');
var R = require('ramda');
var S = require('./service');

// S.getTweets :: UserId -> Promise [Tweet]
// S.getUserName :: UserId -> Promise String
// S.getUserPhoto :: UserId -> Promise String

//  makeUser :: (UserId, String, String) -> User
var makeUser = function(id, name, photo) {
  return { id: id, name: name, photo: photo };
};

//  selectUserId :: Tweet -> UserId
var selectUserId = function(tweet) {
  return tweet.userId;
};

//  selectMessage :: Tweet -> String
var selectMessage = function(tweet) {
  return tweet.msg;
};

//  getUser :: UserId -> Promise User
var getUser = function(userId) {
  // Promise String
  var nameP = S.getUserName(userId);
  // Promise String
  var photoP = S.getUserPhoto(userId);
  return P.liftp3(makeUser)(P.purep(userId), nameP, photoP);
};

//  getTweetsByUserId :: UserId -> Promise [String, User]
var getTweetByUserId = function(theId) {
  // Promise [Tweet]
  var tweetsP = S.getTweets(theId);
  // UserId -> Promise User
  var getUserCached = R.once(getUser);
  // Tweet -> Promise [String, User]
  var getTweetByUserId = function(tweet) {
    // UserId
    var userId = selectUserId(tweet);
    // String
    var message = selectMessage(tweet);
    // Promise User
    var cachedUserP = getUserCached(userId);
    return P.liftp2(R.pair)(P.purep(message), cachedUserP);
  };
  return P.liftp1(P.traversep(getTweetByUserId))(tweetsP);
};

getTweetsByUserId(1)
.then(function(tweets) {
  console.log('tweets:', tweets);
})
.catch(function(err) {
  console.log('fail to fetch tweets', err);
});