How do we pass parameters to a mounted route in nodeJS?

Question

I'm taking a course on NodeJS, there were a few assignments related to routing, everything works fine except this part which seems a little odd: For some reason, I cannot read the parameter ID being passed to the mounted router.

dish.js

const express = require('express');
const bodyParser = require('body-parser');
const dishRouter = express.Router();

dishRouter.use(bodyParser.json());

dishRouter.route('/')
.all((req,res,next) => {
    res.statusCode = 200;
    res.setHeader('Content-Type','text/plain');
    next();
})
.get((req,res) => {
    console.info('Info: ',req);
    res.end(`Sending details of the dish back to you: ${req.params.dishId}`);
})
.post((req,res) => {
    res.statusCode = 403;
    res.end(`Operation not supported: ${req.params.dishId}`);
})
.put((req,res) => {
    res.write(`Updating the dish...: ${req.params.dishId} \n` );
    res.end(`Will update this dish: ${req.body.name} with details: ${req.body.description}`);
})
.delete((req,res) => {
    res.end(`Deleting this dish: ${req.params.dishId}`);
});

exports.dish = dishRouter;

dishes.js

const express = require('express');
const bodyParser = require('body-parser');
const dishesRouter = express.Router();

dishesRouter.use(bodyParser.json());

dishesRouter.route('/')
.all((req,res,next) => {
    res.statusCode = 200;
    res.setHeader('Content-Type','text/plain');
    next();
})

.get((req,res) => {
    res.end('Sending all dishes back to you');
})  

.post((req,res) => {
    res.end(`Will add the dish: ${req.body.name} with details: ${req.body.description}`);
})

.put((req,res) => {
    res.statusCode = 403;
    res.end(`Operation not supported.`);
})

.delete((req,res) => {
    res.end(`Deleting all dishes.....`);
});

exports.dishes = dishesRouter;

index.js

const express = require('express');
const morgan = require('morgan');
const bodyParser = require('body-parser');
const http = require('http');
const dishRouter = require('./routes/dish');
const dishesRouter = require('./routes/dishes');
const hostname = 'localhost';
const port = 3000;

const app = express();
app.use(morgan('dev'));
app.use(bodyParser.json());

app.use('/dishes',dishesRouter.dishes);
app.use('/dishes/:dishId',dishRouter.dish);

app.use(express.static(__dirname+'/public'));

app.use((req,res,next) => {
    res.statusCode = 200;
    res.setHeader('Content-Type','text/html');
    res.end('<html><body><h1>This is an Express Server</h1></body></html>');
});

const server = http.createServer(app);

server.listen(port,hostname,(req,res) => {
   console.info(`Server running on port: ${port}, at: ${hostname}`);
})

This GET localhost:3000/dishes/123 is calling the right route, but the parameter dishId comes back as "undefined". Again, just learning nodeJS, seems like my receiver/mounted route should receive those parameters just fine, the body can be read properly, but not the params. ... thanks.

Bergur · Accepted Answer · 2020-09-09T23:12:26.917

Yeah the params don't flow between routers. You're on a new router, hence new route params object.

You can check out the code for this: https://github.com/expressjs/express/blob/master/lib/router/index.js#L43 Check out line 43 and line 53 where route.params is set to an empty object.

Some examples:

index.js

app.use('/dishes/:dishId',(req, res) => {
  console.log('now I get my dishId', req.params.dishId)
});

dish.js (version 1)

dishRouter.route('/')
.get((req, res) => {
  console.log('now i get nothing', req.params)
})

dish.js (version 2)

dishRouter.route('/:anotherId')
.get((req, res) => {
  console.log('now we get another parameter', req.params.anotherId)
})
// the path would be /dish/123/456

I'm not sure if there is a offical-expressjs-way to pass the params object between routers.

One solution would be to create a custom handler

index.js

app.use('/dishes/:dishId', handler)

handler.js

function handler (req, res, next) {
  if (req.method === 'GET') {
    console.log('now we get it', req.params)
  }
}

module.exports = handler

Anoter way would be to add the dishId to the request object before calling the router:

index.js

app.use('/dishes/:dishId', (req, res, next) => {
  req.dishId = req.params.dishId
  router(req, res, next)
})

dish.js

const express = require('express')
const router = express.Router()
  router.route('/')
  .get((req, res) => {    
    console.log('nothing here', req.params)
    console.log('dishId', req.dishId)
  })

module.exports = router

Third way would be to send the params as options to a router function

index.js

app.use('/dishes/:dishId', (req, res, next) => {
  router(req.params)(req, res, next)
})

dish.js

function createRouter (options) {
  const router = express.Router()
  router.route('/')
  .get((req, res) => {    
    console.log('nothing here', req.params)
    console.log('but alot here', options)
  })

  return router
}

module.exports = createRouter

If you want you could also just put the :dishId on the router as an optional parameter

index.js

app.use('/dishes', dishesRouter)

dishes.js

const express = require('express')
const router = express.Router()

router.route('/:dishId?')
  .get((req, res) => {        
    if (req.params.dishId) {
      res.end(`Sending details of the dish back to you: ${req.params.dishId}`)
    } else {
      res.end('Sending all dishes back to you');
    }
  })

module.exports = router

Thanks, I went with your option (below). I figured, it's just a singleton anyways, I could just pass the caught param that way as you well put it. (thanks) app.use('/dishes/:dishId', (req, res, next) => { req.dishId = req.params.dishId router(req, res, next) }) — Mike Gmez, Sep 10 '20 at 05:23

How do we pass parameters to a mounted route in nodeJS?

1 Answers1