This feature is non-standard and is not on a standards track. Do not use it on production sites facing the Web: it will not work for every user. There may also be large incompatibilities between implementations and the behavior may change in the future.
.value read-only property returns an
ArrayBuffer containing the currently cached descriptor value. This value gets updated when the value of the descriptor is read.
var characteristic = BluetoothRemoteGATTDescriptor.characteristic
The definition of 'value' in that specification.