An Express router provides a subset of Express methods. To create an instance of one, we invoke the .Router() method on the top-level Express import.

To use a router, we mount it at a certain path using app.use() and pass in the router as the second argument. This router will now be used for all paths that begin with that path segment. To create a router to handle all requests beginning with /monsters, the code would look like this:

const express = require('express'); const app = express(); const monsters = { '1': { name: 'godzilla', age: 250000000 }, '2': { name: 'manticore', age: 21 } } const monstersRouter = express.Router(); app.use('/monsters', monstersRouter); monstersRouter.get('/:id', (req, res, next) => { const monster = monsters[req.params.id]; if (monster) { res.send(monster); } else { res.status(404).send(); } });

Inside the monstersRouter, all matching routes are assumed to have /monsters prepended, as it is mounted at that path. monstersRouter.get('/:id') matches the full path /monsters/:id.

When a GET /monsters/1 request arrives, Express matches /monsters in app.use() because the beginning of the path ('/monsters') matches. Express’ route-matching algorithm enters the monstersRouter‘s routes to search for full path matches. Since monstersRouter.get('/:id) is mounted at /monsters, the two paths together match the entire request path (/monsters/1), so the route matches and the callback is invoked. The 'godzilla' monster is fetched from the monsters object and sent back.



Create an expressionsRouter instance of Express.Router. Mount it at /expressions at your base app level with app.use.

After doing so, create a route for your expressionsRouter that will send all expressions for a GET request.

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