[Feature Request] JavaScript: stable error codes

[vyacheslav-sozap]

Right now, catching errors from Nakama JavaScript API looks like this:

try {
    nk.linkDevice(userId, deviceId);
} catch (e) {
    if (e.message == 'error linking: rpc error: code = AlreadyExists desc = Device ID already in use.') {
        //make processing
    }
}

Obviously, the problem with such code is that message format might (and already did) change on Nakama update, so it would be nice to have some error code inside throwable object.