Firebase Docs Reference Interface: Change functions.Change interface static The Functions interface for events that change state, such as Realtime Database or Cloud Firestore onWrite and onUpdate. Properties after non-null Object Represents the state after the event. before non-null Object Represents the state prior to the event. Except as otherwise noted, the content of this page is licensed under the Creative Commons Attribution 3.0 License, and code samples are licensed under the Apache 2.0 License. For details, see our Site Policies. Java is a registered trademark of Oracle and/or its affiliates. Last updated April 3, 2018.