Callbacks vs promises

chaining.js

var driverDetailsPromise = Driver.findWithPromises({_id:req.params.id}).then(function(drivers){
  return drivers[0];
})

drivers.js

var OPEN_STATUS = "open";
var Driver = require('../models/driver');
var Request = require('../models/request');

Driver.find({name : 'rajiv'}, function(error, drivers) {
  if (error) {
    response.status(500).send(error);
  }
  var firstDriver = drivers[0];
  Request.find({driver_id : firstDriver._id}, function(error, requests) {
    if (error) {
      response.status(500).send(error);
    }
    var firstRequest = requests[0];
    Request.findByIdAndUpdate(firstRequest._id, {$set:{status:OPEN_STATUS}}, function(error, updatedRequest) {
      if (error) {
        response.status(500).send(error);
      }
      response.status(200).send(updatedRequest);
    })
  });
});

Driver.findWithPromises({name : 'rajiv'}).then(function(drivers) {
  return drivers[0];
}).then(function(firstDriver){
  return Request.findWithPromises({driver_id : firstDriver._id});
}).then(function(error, requests) {
  return requests[0];
}).then(function(firstRequest) {
  return Request.findByIdAndUpdateWithPromises(firstRequest._id, {$set:{status:OPEN_STATUS}});
}).then(function(updatedRequest) {
  response.status(200).send(updatedRequest);
}).catch(function(error){
  response.status(500, error);
});

MultiplePromises.js

var driverDetailsPromise = Driver.findWithPromises({_id:req.params.id}).then(function(drivers){
  return drivers[0];
})

var tripsByDriverPromise = Request.findWithPromises({driver_id:req.params.id});

Promise.all([driverDetailsPromise, tripsByDriverPromise]).then(function(results){
  var firstDriverDetails = results[0];
  var tripsByDriver = results[1];
  response.status(200).send({'details': firstDriverDetails, 'trips' : tripsByDriver});
});

Simple promise.js

var promise = new Promise(function(resolve, reject) {
  setTimeout(function() {
    resolve("Hello World")
  }, 2000);
});

promise.then(function(text) {
  console.log(text);
});