[Home](./index.md) > [sip.js](./sip.js.md) > [TransactionUser](./sip.js.transactionuser.md) > [onStateChange](./sip.js.transactionuser.onstatechange.md) ## TransactionUser.onStateChange property Callback for notification of transaction state changes. Not called when transaction is constructed, so there is no notification of entering the initial transaction state. Otherwise, called once for each transaction state change. State changes adhere to the following RFCs. https://tools.ietf.org/html/rfc3261\#section-17 https://tools.ietf.org/html/rfc6026 Signature: ```typescript onStateChange?: (newState: TransactionState) => void; ```