How to delay execution until condition is met?

Question

Node.js

The endpoint "/search" receives a variety of data from filters. I include the incoming data in the query object, the reserveNomersIds array is filled if the data arrived by date. How to delay the execution of Nomer.find(query) until reserveNomerIds is filled, that is, the if (req.body.from && req.body.to) condition is checked?

app.post('/api/search', function(req, res) {
        var query = {}
        var reserveNomersIds;
        var filter = {}

        //price
        if (req.body.min && req.body.max) {      
            query.cost_per_night = {$gte: req.body.min, $lte: req.body.max}
            //по возрастанию
            filter.cost_per_night = 1
        }
        //dates
        if (req.body.from && req.body.to) {
            Reservation.distinct("nomer", {from: {$lt: new Date(req.body.to)}, to: {$gt: new Date(req.body.from)} }
            ).then((data, err) => {
                reserveNomersIds = data;
            })
        }
        if (req.body.guests > 1) {
            query.occupancy = {$gte: req.body.guests}
        }
        if (req.body.search) {
            query.city = { $regex: req.body.search.toLowerCase() }
        }
        Nomer
            .find({ _id: { $nin: reserveNomersIds}, query})
            .sort(filter)
            .then(function (err, result) {
                if(err){
                    res.send(err);
                } else {
                    res.json(result);
                }
            })
    })

Answer 1

Is it not possible in modern Javascript?

app.post('/api/search', async function(req, res) {
  var query = {}
  var reserveNomersIds;
  var filter = {}

  //price
  if (req.body.min && req.body.max) {
    query.cost_per_night = {$gte: req.body.min, $lte: req.body.max}
    //по возрастанию
    filter.cost_per_night = 1
  }
  //dates
  if (req.body.from && req.body.to) {
    reserveNomersIds = await Reservation.distinct("nomer", {
      from: {
        $lt: new Date(req.body.to)},
        to: {$gt: new Date(req.body.from)
      }
    });
  }
  if (req.body.guests > 1) {
    query.occupancy = {$gte: req.body.guests}
  }
  if (req.body.search) {
    query.city = { $regex: req.body.search.toLowerCase() }
  }
  try {
    var result = await Nomer
      .find({ _id: { $nin: reserveNomersIds}, query})
      .sort(filter);

    res.json(result);
  } catch (e) {
    res.send(e);
  }
})