## Table of Contents - [[#Express router]] - [[#Controllers]] - [[]] - [[]] ### `res`, `res` `req` and `res` are objects containing information about the http request and response, respectively. From `req` we are able to glean certain information related to the http request, such as the client's IP address, info about the client's browser, etc. (basically, all of the info from [[HTTP#^85025d|the request headers]]). The `res` object is all of the stuff the server sends back. Generally speaking (oversimplification), in Express, we *get stuff* out of the `req` object, and *add things* to the `res` object. ### Express router Express router is a like a mini Express app. It helps with modularization. ### Controllers Controllers in Express refer to collections of middleware functions typically grouped around a specifc topic `app.use` means any request can access the passed-in endpoint ```js // route all requests to `/articles` endpoint to articleRouter file app.use('/articles', articleRouter) ``` If we pass an argument to `next()`, that goes to the global error handler. ### Middleware [Middleware functions in Express](https://expressjs.com/en/guide/writing-middleware.html) ___ **Tags**: