This feature is obsolete. Although it may still work in some browsers, its use is discouraged since it could be removed at any time. Try to avoid using it.
BluetoothDevice.gattServer read-only property returns a reference to the device's GATT server or null if the device is disconnected.
var gattServer = instanceOfBluetoothDevice.gattServer
A reference to the device's GATT server or null if the device is disconnected.
The definition of 'gattServer' in that specification.