Try to understand how to use `spread` in Q - a tool to compose asynchronous promises.

spread.js

var Q = require('q');
var util = require('util');

function randomDelayedCall(func) {
  var delay = Math.floor(Math.random() * (1200 - 100) + 100);
  setTimeout(func, delay);
}

function findUser(id, cb) {
  var err = null;
  // err = new Error('Cannot find the user with id: ' + id);
  var name = 'Kate';
  if (0 === id % 2) {
    name = 'Bob';
  }
  randomDelayedCall(function() {
    cb(err, name);
  });
}

function jsonify(name, cb) {
  var jsonString = '{"name": "' + name + '"}';
  var result = JSON.parse(jsonString);
  var err = null;
  randomDelayedCall(function() {
    cb(err, result);
  });
}

function sendResult(jsonData, cb) {
  var err = null;
  // err = new Error('Cannot send result!');
  randomDelayedCall(function() {
    console.log('Result:', util.inspect(jsonData));
    cb(err);
  });
}

function save(name, cb) {
  var err = null;
  randomDelayedCall(function() {
    console.log('Saved to DB.');
    cb(err);
  });
}

// Q.nfcall(findUser, 4)
//   .then(function(name) {
//     console.log('Found user:', name);
//     return Q.nfcall(save, name).then(function() {
//       return Q.nfcall(jsonify, name);
//     });
//   })
//   .then(function(jsonData) {
//     return Q.nfcall(sendResult, jsonData);
//   })
//   .then(function() {
//     console.log('Finished');
//   })
//   .fail(function(error) {
//     console.error('Error occurred: ', error);
//   });

/* by using spread, get the same result as above */
Q.nfcall(findUser, 5)
  .then(function(name) {
    console.log('Found user:', name);

    return [name, Q.nfcall(jsonify, name)];
  })
  .spread(function(name, jsonData) {
    return [Q.nfcall(save, name), Q.nfcall(sendResult, jsonData)];
  })
  .spread(function() {
    console.log('Finished.');
  })
  .fail(function(error) {
    console.error(error);
  });
// Call done() if you don't have a failed handler,
// the errors will be thrown to outside.
// Otherwise, the errors are swallowed.
// .done();