OK, @vhymanskyy I cleared out all remnants of node, nodejs & npm that I could find, including any in
/usr/bin, so I could start from relative scratch. I did not remove any Blynk directories as I didn't know which ones were related to my wiringPi install.
I then re-ran through your entire list of commands again... and the only warnings were at the very last install...
root@raspberrypi:~# npm install -g blynk-library onoff
/opt/nodejs/bin/blynk-client -> /opt/nodejs/lib/node_modules/blynk-library/bin/blynk-client.js
/opt/nodejs/bin/blynk-ctrl -> /opt/nodejs/lib/node_modules/blynk-library/bin/blynk-ctrl.js
> email@example.com install /opt/nodejs/lib/node_modules/onoff/node_modules/epoll
> node-gyp rebuild
gyp WARN EACCES user "root" does not have permission to access the dev dir "/root/.node-gyp/6.9.5"
gyp WARN EACCES attempting to reinstall using temporary dev dir "/opt/nodejs/lib/node_modules/onoff/node_modules/epoll/.node-gyp"
make: Entering directory '/opt/nodejs/lib/node_modules/onoff/node_modules/epoll/build'
make: Leaving directory '/opt/nodejs/lib/node_modules/onoff/node_modules/epoll/build'
Unfortunately, after running the
blynk-client <auth> command, I still have the same null result... no errors or delays before jumping back to the CLI prompt.