• Routing is all about handling routes, .i.e URL paths. What to do/present/show when someone goes to a route (aka a URL or a path)
  • routes are URL handling code
// Route definition structure
  • The METHOD could be any http method (GET, POST, PUT, DELETE etc.). You can also use all as a catchall for any method supported in the http module (it’ll execute the handler for the URL regardless of the method you are using) app.all(PATH, HANDLER)
  • The HANDLER could be a callback function, or a file (module) that has the router defined (containing all the routes)
// Routing in Express.js
// path: ./routes/index.js
const express = require('express');
const router = express.Router();

router.get('/', (request, response) => {
  response.send('Hey it works!');

module.exports = router;
// path: ./app.js
const routes = require('./routes/index'); // import our routes

app.use('/', routes); // use the routes file whenever anyone goes to /anything
app.use('/admin', adminRoutes); // You can have multiple route handlers

Callback / Handlers

app.all('/secret', (request, response, next) => {
  next() // pass control to the next handler

In the response (it doesn’t have to be called response, it’s just a variable name you’ll use inside the function, you can call it dodo for all that matters, but you’ll most commonly see it defined as res), you can:

  • console.log() things
  • send back text .send()
  • send back JSON data .json()
  • if you send data twice (e.g. using both .send() and .json()), you’re gonna get headers are already sent. So make sure you’re never sending data more than once.
  • next is for when you don’t want to send any data back or want to pass it along to something else
router.get('/', (req, res) => {
  let profile = { name: 'Aamnah', age: 100, cool: true };
  console.log('chal gya!');
  res.send('chal gya code');
  • request.query() access Query strings
  • request.params() access URL Parameters
  • request.body() access POSTed values

Query strings

From the request you can extract any data that was passed via the URL

For example:

router.get('/', (req, res) => {
  res.send(req.query); // {"name":"\"Aamnah\"","age":"100"}
  res.send(; // Aamnah
  res.send(req.query.age);  // 100

req.query is an object full of all the query parameters


  • : specifies parameters
router.get('/profile/:name', (req, res) => { // :name is a variable

Now it’ll handle URLs in the structure of /profile/whomever, where whomever is the value of the name parameter. You can access these parameters values like so:

router.get('/profile/:name/:role', (req, res) => { //
  res.send(`${}'s role is ${req.params.role}`); // aamnah's role is admin

Here’s some code to reverse any string sent to a URL endpoint

router.get('/reverse/:string', (request, response) => { // localhost:port/reverse/aamnah is awesome
  let reverse = [...request.params.string].reverse().join(''); // using ES6 spread syntax here
  response.send(reverse); // emosewa si hanmaa