Right now the only way to listen for changes on the server is through the Node.js SDK provided in the professional/enterprise editions. The open-source Node.js SDK does not support opening/writing/listening to synchronized Realms.

This is extremely helpful feedback, as we have been exploring how to expose this functionality at lower prices or in the free developer edition. One option would be to include the ability to register listeners through the dashboard similar to AWS Lambda. Would that help?