Some questions around Bluetooth Server

why do we use writable instead of writeable ? It took three coffee during test to recognize the missing e.

I don't know - but going by Google results, writable is about 4x more popular than writeable, so it seems like a good one to use. Maybe writable is an americanism?

the only event for a service is onWrite. Is there a reason not to use onRead ? I've added this during test for ESP32

Can we detect that? If so we could add it - although there haven't been any requests for that functionality :)

is there an option to define type of value for "mySpecialService" ? This can be done with a descriptor, but how would I define in javascript ? NRF connect supports byte, uint, text and some others.

Do you have an example? I assumed all you could define (that was actually exported via BLE) was the length and UUID.

how would I define writeable for value only, and not for description ?

I'm not sure I understand. You can't specify a description at the moment as far as I know.

how would I read or write value of a characteristic?

A characteristic that you defined? You can't read it as far as I know (I don't think I can get that info from the Nordic softdevice), but you can use NRF.updateServices to update them. Ideally I guess it'd return a BluetoothGATTCharacteristic or something, but it's hard to do that while also allowing the user to specify data with a simple { .. }.