Data Not Syncing

I have tried below code. this is writing data only in localdb. it is not syncing back to the actual db. what are other steps required to sync localdata to actal database.??

const Realm = require('realm');

// Define your models and their properties
const CarSchema = {
  name: 'Car',
  properties: {
    make:  'string',
    model: 'string',
    miles: {type: 'int', default: 0},
  }
};
const PersonSchema = {
  name: 'Person',
  properties: {
    name:     'string',
    birthday: 'date',
    cars:     'Car[]', // a list of Cars
    picture:  'data?'  // optional property
  }
};

Realm.open({schema: [CarSchema, PersonSchema]})
  .then(realm => {
    // Create Realm objects and write to local storage
    realm.write(() => {
      const myCar = realm.create('Car', {
        make: 'Honda',
        model: 'Civic',
        miles: 1000,
      });
      myCar.miles += 20; // Update a property value
    });

    // Query Realm for all cars with a high mileage
    const cars = realm.objects('Car').filtered('miles > 1000');

    // Will return a Results object with our 1 car
    cars.length // => 1

    // Add another car
    realm.write(() => {
      const myCar = realm.create('Car', {
        make: 'Ford',
        model: 'Focus',
        miles: 2000,
      });
    });

    // Query results are updated in realtime
    cars.length // => 2

    // Remember to close the realm when finished.
    realm.close();
  })
  .catch(error => {
    console.log(error);
  });

You seem to be closing the Realm instance immediately after writing the data - can you try to add await realm.syncSession.uploadAllLocalChanges()? With promises should probably look something like:

...
return realm.syncSession.uploadAllLocalChanges().then(() => {
    realm.close();
});