Getting an error on RESTful API?

I am creating a NODEJS RESTful API and when I do npm run install I get an error:

[nodemon] app crashed - waiting for file changes before starting...

and here is my code for my server.

 var express = require('express'),
 app = express(),
 port = process.env.PORT || 3000,

 app.listen(port);

console.log('todo list RESTful API server started on: ' + port);

via D.W