Async.js and Node.js

UserQuery.js

var async = require('async');

// Waterfall through callbacks using Mongoose to query for a user

  async.waterfall([
    function(callback) {
      /** Function 1. Find User.
        * Pass `user` to Function 2.
        */
      User.findOne({ username: 'fred' }, function(error, user) {
        if (error) throw error;
        callback(error, user);
      });
    },
    /** Function 2. Receive User.
      * Pass `user` to final function
      */
    function(user, callback) {
      callback(user);
    }
  ], function(user) {
    // Final function
    console.log(user);
  });

Thanks