missing return breaks the promise chain and causes subtle bugs

missing-return.js

var q = require("q");

var getUser = function(username) {
  return q.delay(500).then(function(){
    return username + " user";
  });
};

var getTweets = function(user) {
  return q.delay(500).then(function(){
    return ["tweet1", "tweet2"];
  });
};

getUser("tom")
  .then(function(user) {
    getTweets(user)
  })
  .then(function(tweets) {
    console.log("tweets: ", tweets);
  });