Generally, we will keep each router in its own file, and require them in the main application. This allows us to keep our code clean and our files short.

To do this with monstersRouter, we would create a new file monsters.js and move all code related to /monsters requests into it.

// monsters.js
const express = require('express');
const monstersRouter = express.Router();

const monsters = {
  '1': {
    name: 'godzilla',
    age: 250000000
  },
  '2': {
    Name: 'manticore',
    age: 21
  }
}

monstersRouter.get('/:id', (req, res, next) => {
  const monster = monsters[req.params.id];
  if (monster) {
    res.send(monster);
  } else {
    res.status(404).send();
  }
});

module.exports = monstersRouter;

This code contains all the monsters specific code. In a more full-fledged API, this file would contain multiple routes. To use this router in another file, we use module.exports so that other files can access monstersRouter. The only other new line of code required is that Express must be required in each file, since we’ll need to create a router with express.Router().

Our main.js file could then be refactored to import the monstersRouter:

// main.js
const express = require('express');
const app = express();
const monstersRouter = require('./monsters.js');

app.use('/monsters', monstersRouter);

In this example, the monstersRouter is required in main.js from monsters.js and used exactly as it was before.