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NodeJs Express tutorial
PixelNinja (319)

NodeJs Express Basics! YAY

Welp, I'm back! posting again, this time, I have got some web server basics. Even if you already know what Express is and how to use it, read along and maybe learn something!

Onto The Basics!


First off, after creating your repl, you will want to install Express, if you create an Express repl, it will already be installed with a template. Otherwise, if you just clicked nodejs, you will need to install it, this can be done through 2 methods:


Open shell (ctrl or cmd + shift + s)
Type in the shell: npm install express
Now you're ready to code!


You can also auto-install it by just using require('express') which we will cover later!

Onto the main code...

You will need to import packages that we will be using. If you are editing on repl.it, packages will auto install, otherwise, please follow steps above for body-parser. Most editors will auto install packages when they are needed some won't so keep this in mind.

Sorry about all that boring stuff, onto the actual code, remember that all the code is at the bottom of the post!


const express = require('express'); 
 Imports the express library.
 This is necessary to have an express server.
const bodyParser = require('body-parser');  // Node.js body parsing middleware.

Just some basic variable setting!

Creating the app / server

We need to turn our express into an app

const app = express(); 

## Telling the app what modules / packages to use

// Express modules / packages

app.use(bodyParser.urlencoded({ extended: true })); 
// Express modules / packages

 // load the files that are in the public directory

app.listen(3000, () => { // Listen on port 3000
    console.log('Listening!') // Log when listen success

Most of this stuff is standard for any express project!

Serving a file

To pick up when someone visits a directory we use app.get()

This will run when someone makes a get request to the url. We will cover other request types later. Here is an example:

app.get('/', (req, res) => {

When someone visits the root or / directory of the site, this function will run if it recieves a get request.

The req, res will let us use the request data and response data. res has lots of functions in which let us send headers to the client.

Here are some:

app.get('/res', (req, res) => {
	/* Please note that this will error as multiple headers are sent to the client */
	// or


	//using res.send(200) is deprecated and will terminate the nodejs in future.




If you get an error about cannot send headers to the client after they are already sent this is because if you use 2 res functions then it will cause this error.

Using req

Query strings are the data included in the url and in the headers. these can be got server side, using req.query as showed below.

app.get('/req', (req, res) => { 
	res.json(req.query) //send json to the client

the console.log, logs all query strings such as '?hello=hi&ping=pong' you can get these through req.query.hello or req.query.ping.

res.json sends json to the client. often used in APIs.

Handling Request Types

There are many request types used for different things:

app.get('/get', (req, res) => {
	// On get request

app.post('/post', (req, res) => {
	// On post request

There are hundreds. Some can be found here
Only some are supported by express.

Handeling multiple methods is easy:

  .get(function (req, res) {
  .post(function (req, res) {
  .put(function (req, res) {


Long Paths

You can have multiple paths like this:

app.get('/multiple/paths', (req, res) => {
	// exist


Make sure you put these at the bottom, as anything that isn't triggered, will run this:

app.get('/multiple/paths/also/work/*', (req, res) => {
	// used for 404 if no other get functions are triggered in this path

app.get('/*', (req, res) => {
	// used for 404 if no other get functions are triggered


When making a server, you need to get it to listen on a port so that the internet can go to your page! We do this with app.listen() and the port goes into the brackets. If you get any problems starting your repl, try changing the port.

Common ports are:

  • Port 80 for HTTP connections
  • Port 443 for HTTPS connections
  • Port 8080 is for other purposes

Repl.it normally blocks 2/3 digit ports but you can try anyways. Here is a bigger list: https://en.wikipedia.org/wiki/List_of_TCP_and_UDP_port_numbers


This has been just the basics but make sure you read other posts! Hope you enjoyed it!

Any questions feel free to ask!

AaronActu (3)

First of all, thanks for this tuto @RossJames ;)

I can't find how to access a route in my repl. For eg, I want to access the route: /mypath?info=somedatas. Is it possible with a REPL ?

PixelNinja (319)

@AaronActu anything is possible with replit! Yes, you can use if statements to check req.query (get question mark data, msg any problems

Dunce (65)

Hello, I'm having trouble getting this to work. It's not giving me an option to visit my website, and if I type in the URL manually it gets stuck on "repl waking up..."
Here's my code

PixelNinja (319)

Hey @Dunce !

I see the problem. I forgot to add that you need to get the server to listen!

Add this code at the bottom:

app.listen(3000, () => {

Edit: I have also added this to the guide

Highwayman (1482)

Yay indeed! Thanks for this.