routes-in-expressjs.md

Routes in Express

On my journey to learn Node.js, I have started to learn about Express framework by exploring how its routing system works. Below is a really simple Hello World app that accepts two routes, a GET and POST request to the root of the directory.

var express = require('express');
var app = express();

// GET request to root of the project
app.get('/', function (req, res) {
  res.send('GET request to the homepage');
});

// POST request to root of the project
app.post('/', function (req, res) {
  res.send('POST request to the homepage');
});

app.listen(3000, function () {
  console.log('Example app listening on port 3000!');
});

Now let's look at some more Express routing examples.

Specific page route

// Matches /about
app.get('/about', function (req, res) {
  res.send('about');
});

Route with parameter

app.get('/user/:id', function (req, res) {
  res.send('user with ID - ' + req.params.id);
});

Using subset of RegEx for route matching

Either /acd or /abcd will be matched

app.get('/ab?cd', function(req, res) {
  res.send('ab?cd');
});

/abcd, /abbcd, /abbbcd and so on will be matched.

app.get('/ab+cd', function(req, res) {
  res.send('ab+cd');
});

/ab(anything random)cd will be matched.

app.get('/ab*cd', function(req, res) {
  res.send('ab*cd');
});

Matches either /abe or /abcde.

app.get('/ab(cd)?e', function(req, res) {
  res.send('ab(cd)?e');
});

Matches anything with an a in the route name

app.get(/a/, function(req, res) {
  res.send('/a/');
});

Accepts any route that ends with fly i.e. /dragonfly, /butterfly, not flydragon.

app.get(/.*fly$/, function(req, res) {
  res.send('/.*fly$/');
});

Callbacks

More than one callback function can handle a route (make sure you specify the next object). For example:

app.get('/next-example', function (req, res, next) {
  console.log('the response will be sent by the next function ...');
  next();
}, function (req, res) { // this is the declared `next` function
  res.send('Hello from B!');
});

Also, an array of callbacks can handle a route as such:

var callback0 = function (req, res, next) {
  console.log('Callback0 here!');
  next();
}

var callback1 = function (req, res, next) {
  console.log('Callback 1, yo ;)');
  next();
}

var callback2 = function (req, res) {
  res.send('Hello from `next example`!');
}

app.get('/callbacks-example', [callback0, callback1, callback2]);

A combination of independent functions and arrays of functions can handle a route as well. For example:

var callback0 = function (req, res, next) {
  console.log('Callback0 calling..');
  next();
}

var callback1 = function (req, res, next) {
  console.log('Callback1 saying hi!');
  next();
}

app.get('/another-callbacks-example', [callback0, callback1], function (req, res, next) {
  console.log('the response will be sent by the next function ...');
  next();
}, function (req, res) {
  res.send('Hello from `another callbacks example`!');
});

Chainable route handlers

Chainable route handlers enable a somewhat cleaner definition of routes when same route handles different types of HTTP requests. It's done by chaining appropraite functions onto app.route().

Below is an example of chained route handlers that are defined by using app.route():

app.route('/book')
  .get(function(req, res) {
    res.send('Get a random book');
  })
  .post(function(req, res) {
    res.send('Add a book');
  })
  .put(function(req, res) {
    res.send('Update the book');
  });

Resources

• Express routing