https://frankl.in/code/before-exit-scripts-in-node-js

exit.js

// Add pre-exit script
process.on ('exit', code => {
  console.log (`Whoa! Exit code ${code}, cleaning up...`);
  // i.e. close database
});

// Add another for fun
process.on ('exit', code => {
  if (code > 0) {
    console.log ('Hmm something went wrong');
  } else {
    console.log ('And done!');
  }
});

console.log ('App ready.');
console.log ('Doing app stuff...');