If you're using a testing framework like Mocha, or a development server that automatically reloads on changes, requiring the same file multiple times can cause problems. For example, if you've got an app.js file that runs your server, then each time it's reloaded it will register new routes and endpoints. I have to get top writing services online to complete my work. If you require() a module from within the app.js file, then each time the file is loaded another instance of that module will be created. You might want to make sure your routes are only registered once.