Unable to run node app.js file

try npm start from testsite directory.

look at the package.json

scripts : { start : node bin/www }

So you must execute the www under the bin directory.

So instead of node app.js use node bin/www

You have to add this code to app.js file, this will tell express to listen on port 3000 and display a log message

 app.listen(3000, function () {
console.log("Express server listening on port 3000");
});

Try running nodejs app.js instead of node app.js