problem with scope of variable callback

callback_problem.js

function getAllCity(req, res) {
  var promise = Q.fcall(function() {
    return City.find({}, function(err, cities) {
      if(err) {
        console.log(err);
        return res.send(404)
      }
      for (let i = 0; i < cities.length; i++) {
        Location.findOne({_id : cities[i].locationId}, function(err, location){
          if(err) return;
          cities[i].locationLng = location.lng;
          cities[i].locationLat = location.lat;
        });
      }
    });
  });
  promise.then(function(data) {
    console.log(data);
  }, function(err) {
    console.log(err);
  });
  // return res.json({isSucess: true, data: cities})
};

function getAllCity(req, res) {
  var promise = Q.fcall(function() {
    return City.find({}, function(err, cities) {
      if(err) {
        console.log(err);
        return res.send(404)
      }
      let tasks = [];

      for (let i = 0; i < cities.length; i++) {
        tasks.push(Location.findOne({_id : cities[i].locationId}, function(err, location){
          if(err) return;
          cities[i].locationLng = location.lng;
          cities[i].locationLat = location.lat;
          return cities[i];
        }));
      }
      return Q.all(tasks);
    });
  });
  promise.then(function(data) {
    console.log(data);
  }, function(err) {
    console.log(err);
  });
  // return res.json({isSucess: true, data: cities})
};

function getAllCity(req, res) {
  var promise = City.find({}, function(err, cities) {
      if(err) {
        console.log(err);
        return res.send(404)
      }
      let tasks = [];

      for (let i = 0; i < cities.length; i++) {
        tasks.push(Location.findOne({_id : cities[i].locationId}, function(err, location){
          if(err) return;
          cities[i].locationLng = location.lng;
          cities[i].locationLat = location.lat;
          return cities[i];
        }));
      }
      return Q.all(tasks);
    });

  promise.then(function(data) {
    console.log(data);
  }, function(err) {
    console.log(err);
  });
  // return res.json({isSucess: true, data: cities})
};

function getAllCity(req, res) {
  const promise = City.find().then(cities => {
    let tasks = [];
    
    for (let i = 0; i < cities.length; i++) {
      tasks.push(Location.findOne({
        _id : cities[i].locationId
      })
      .then(function(location){
        cities[i].locationLng = location.lng;
        cities[i].locationLat = location.lat;
        return cities[i];
      }));
    }
    
    return Q.all(tasks);
  });
  
  promise.then(cities => {
    res.json({
      isSucess : true,
      data : cities
    });
  })
  .catch(err => {
    res.status(500).send({
      message : err.message
    });
  });
};