BLE : How to use sequence number in an angular app

I have an issue with sequence order when reading data from ble. This issue is referenced here
The version 1.2.4 of cordova-plugin-ble-central has a new parameter to get the sequence order and leave a chance to the client to reorder the packet. The PR is here
How can i use this sequence number in my angular app?
I received an Observable and I don’t see how access this parameter:

this.ble.startNotification(device.handle,
BSC_SERVICE_UUID,
BSC_OUTPUT_CHARACTERISTIC_UUID).subscribe(y => {
         const x = new Uint8Array(y);
         ....
 });