Routing is the process of determining what should happen when a URL is called, or also which parts of the application should handle a specific incoming request.

In the Hello World example we used this code

app.get('/', (req, res) => { /* */ })

This creates a route that maps accessing the root domain URL / using the HTTP GET method to the response we want to provide.

Named parameters

What if we want to listen for custom requests, maybe we want to create a service that accepts a string, and returns that uppercase, and we don’t want the parameter to be sent as a query string, but part of the URL. We use named parameters:

app.get('/uppercase/:theValue', (req, res) => res.send(req.params.theValue.toUpperCase()))

If we send a request to /uppercase/test, we’ll get TEST in the body of the response.

You can use multiple named parameters in the same URL, and they will all be stored in req.params.

Use a regular expression to match a path

You can use regular expressions to match multiple paths with one statement:

app.get(/post/, (req, res) => { /* */ })

will match /post, /post/first, /thepost, /posting/something, and so on.