Step 8: To run the app, add the following at the bottom:

app.listen(3000)

The 3000 is a port number. A server can run many apps at the same time, and they are separated by port numbers. Node apps typically run on port 3000. Type the following on the command line:

node server.js

The server is now running and listening for requests. Simulate a client by opening a browser, and typing the following in the address bar:

localhost:3000

You should see hello world in the browser. If you want to change the message, first stop the app by pressing Ctrl + C on the command line. Then press the up arrow to run the previous command again.