As you saw in the previous exercise, when using routers, it’s important to remember that the full path of a request can be segmented.
In the diagram to the left, you can create an Express application using two routers. A GET request arrives for
/expressions/1. Because the beginning of the path does not match
/animals in the first
app.use(), the Express server moves on to the next
app.use(), which matches
Express’ route matching algorithm then enters the
expressionsRouter instance which is
required from expressions.js. Inside this router, the path matching changes. Even though the whole request path is
/expressions/1, inside the
expressionsRouter, all paths are matched from the parts of the path after
/expressions, meaning that in this context, the router is trying to match the path
Because the path is
/1, the path does not match the first
.get() method at
/. The Express server moves on to the next route, which has a route parameter of
/:id, so it matches! This route handles the necessary logic and sends the response.
Routers can be nested as many times as necessary for an application, so understanding nested route matching is important for created complicated APIs.
Move on to the next exercise when you’re ready.