# Parse push fields (/en/realtime-media/im/build/notifications-and-event-handling/offline-push/parse-push-fields/react-native)

> For AI agents: see the complete documentation index at [llms.txt](/llms.txt).

After receiving a push notification, you need to parse the data.

    Rewrite the `FirebaseMessagingService.onMessageReceived` method to get a custom extension field in the `RemoteMessage` object. The sample code is as follows:

    ```typescript
    messaging().onMessage(async (remoteMessage) => {
      console.log("A new FCM message arrived!", JSON.stringify(remoteMessage));
      // "t":"receiver",
      // "f":"fromUsername",
      // "m":"msg_id",
      // "g":"group_id",
      // "e":{}
    });
    ```

    | Parameter | Description                                              |
    | --------- | -------------------------------------------------------- |
    | `f`       | The user ID of the push notification sender.             |
    | `t`       | The user ID of the push notification recipient.          |
    | `m`       | The message ID: A unique identifier of the message.      |
    | `g`       | The group ID: This field exists only for group messages. |
    | `e`       | The user-defined extension field.                        |

    `e` is a completely user-defined extension. The data source is `em_push_ext.custom` of the message extension. The data structure is as follows:

    ```json
    {
        "em_push_ext": {
            "custom": {
                "key1": "value1",
                "key2": "value2"
            }
        }
    }
    ```

    The data structure of the extension in the `RemoteMessage` object is as follows:

    ```json
    {
      "t": "receiver",
      "f": "fromUsername",
      "m": "msg_id",
      "g": "group_id",
      "e": {}
    }
    ```