gistfile1.js

var step = 0;

async.waterfall([
    function (next){
        step = 1;
        getJson('/user', function(user) { next(null, user); });
    },
    function (user, next){
        step = 2;
        getJson('/twitter_profile', user.twitterId, function(twitterProfile) { next(null, user, twitterProfile); });
    },
    function (user, twitterProfile, next){
        step = 3;
        getJson('/mashup_data', user.mashupRole, twitterProfile.lastTweetTimestamp, function(data) { next(null, user, twitterProfile, mashupData); });
    }
], function (user, twitterProfile, mashupData) {
  if (err) {
    console.log("Died at step:" + step);
  } else {
    console.dir({
      user: user,
      twitterProfile: twitterProfile,
      mashupData: mashupData
    });
  }
});

// vs:

// see: https://gist.github.com/creationix/5544019
run(function* () {
  var user, twitterProfile, mashupData, step = 1;
  try {
    step++;
    user = yield getJson('/user');
    step++;
    twitterProfile = yield getJson('/tiwtter_profile', user.id);
    step++;
    mashupData = yield getJson('/stock_exchange', user.mashupRole, twitterProfile.lastTweetTimestamp);
    console.dir({
      user: user,
      twitterProfile: twitterProfile,
      mashupData: mashupData
    });
  } catch(err) {
    console.log("Died at step:" + step);
  }
})();