You build node.js app with express v4.x then start your app by npm start. My question is how to stop the app? Is there npm stop?
You can use pm2
https://pm2.keymetrics.io/docs/usage/quick-start/
after installation just type in terminal
pm2 start app.js and then
pm2 start app.js
pm2 stop 0 to stop your server
pm2 stop 0