Popular Stackoverflow questions

To help inform writing new documentation "guides," let's examine some of the most popular Express questions asked on Stackoverflow:

• Most frequent questions
• Most-voted questions

There are lots of good questions there; here are a few that are in both lists:

• How to get GET (query string) variables in Express.js on Node.js?
• How to structure an application?
• Related: Breaking up the app.js file
• How to get POST a query
• How to allow CORS?