example.js

                    vehicles.forEach((ownedVehicle) => {
                        VehicleModel.findOne({_id: ownedVehicle.vehicleId}, (err, vehicle) => {
                            if (err) throw err;
                            console.log(vehicle);

                            returnArr.push({
                                year: vehicle.year,
                                make: vehicle.make,
                                model: vehicle.model,
                            });
                            
                            if (returnArr.length === vehicles.length) {
                              resolve(returnArr);
                            }
                        });
                    });