How do I pass a parameter to express.js Router?

Question

Here's a modified example from Express.js's routing guide:

var express = require('express'); var router = express.Router();  router.get('/', function(req, res) {   res.send('Birds home page'); });  router.get('/about', function(req, res) {   res.send('About birds'); });  ... app.use('/birds', router); app.use('/fish', router); 

This prints "About birds" when I visit both /birds/about and /fish/about.

How do I pass a parameter or something to the router so, in the controller functions, it can tell those two different routes apart?

For example, I'd like to see "Birds can fly" when visiting /birds/about and "Fish can swim" when visiting /fish/about.

Ideally, I'd like to be able to pass some "configuration object" so the mini-app does not need to know about all possible routes it may be mounted at (in pseudocode):

    router.get('/about', function(req, res) {       res.send(magic_configuration.about_text);     });    ....    magically_set_config(router, {about_text: "Bears eat fish"})    app.use('/bears', router); 

Answer 1

Here's what I've come up with: I pass the "mini-app configuration" by assigning it to req:

app.use('/birds', function (req, res, next) {     req.animal_config = {         name: 'Bird',         says: 'chirp'     };     next(); }, animal_router);  app.use('/cats', function (req, res, next) {     req.animal_config = {         name: 'Cat',         says: 'meow'     }     next();         }, animal_router); 

and then in my route I can access them:

var express = require('express'); var router = express.Router();  ...  router.get('/about', function(req, res) {   var animal = req.animal_config;   res.send(animal.name + ' says ' + animal.says); }); 

This approach allows to easily mount the "mini-app" at another location providing different configuration, without modifying the code of the app:

app.use('/bears', function (req, res, next) {     req.animal_config = {         name: 'Bear',         says: 'rawr'     };     next(); }, animal_router); 

Answer 2

You're basically talking about injecting configuration to a router.

I have faced with similar problem and figured out that in theory you can export not a router itself, but rather function that accepts configuration and returns created and configured router.

So in your case calling code will look like:

var animal_router = require('./animal_router')  app.use('/birds', animal_router({     name: 'Bird',     says: 'chirp' }));  app.use('/cats', animal_router({     name: 'Cat',     says: 'meow' })); 

While ./animal_router.js might look following:

var express = require('express');  // Create wrapper function that will adjust router based on provided configuration var wrapper = function (animal_config) {     var router = express.Router();          router.get('/about', function(req, res) {         var animal = animal_config;         res.send(animal.name + ' says ' + animal.says);     });      return router; }  module.exports = wrapper;