App

The app object denotes the Express application.

The app object has methods for:

• Routing HTTP requests
  • ex. app.get(), app.param()
• Configuring middleware
  • app.route()
• Rendering HTML views
  • app.render()
• Registering a template engine
  • app.engine()

Express variables

• we can set and get variables that are available throughout express with app.set and app.get
• Express has the concept of the "app settings table", which is essentially a list of key-value pairs for configging Express that we can manipulate with app.set

Local properties

The app.locals object has properties that are local variables within the application. Once set, the value of app.locals properties persist throughout the life of the application,

• can be accessed on req.app.locals

in contrast with res.locals properties that are valid only for the lifetime of the request.