[Home](./index.md) > [@snowplow/react-native-tracker](./react-native-tracker.md) > [SubjectConfiguration](./react-native-tracker.subjectconfiguration.md) > [domainUserId](./react-native-tracker.subjectconfiguration.domainuserid.md) ## SubjectConfiguration.domainUserId property The domain user id (DUID) is a generated identifier that is stored in a first party cookie on Web. The React Native tracker does not assign it automatically. Signature: ```typescript domainUserId?: string; ```