I have a PI3. I have blown it away and started over once. I have gone thru both the web page and the youtube installs. I have verified just one node version installed. I still get this error! I don’t know what mraa is! And I did install onoff via the instructions. I am using a relay module that worked under another program. Side note…see nothing on why you would select an output, then change the two connected boxes. Right now the first has 0, the 2nd has 1. The button sends me the message like clockwork upon pushing and the app stays online (which is a good sign). I have seen previous posts but not working.
Latest Raspbian - all updates.
pi@raspberrypi:~ $ node --version
pi@raspberrypi:~ $ npm --version
pi@raspberrypi:~ $ nodejs --version