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Author: Tianle Yuan




Express.js, or simply Express, is a back end web application framework for building RESTful APIs with Node.js, released as free and open-source software under the MIT License. It has been called the de facto standard server framework for Node.js.


It is designed for building web applications and APIs.


Code using

//declare using Express.js
const express = require('express')
const app = express() 
//app starts a server listens on port 3000 for connections
const port = 3000
//app responds with “Hello World!” for requests to the root URL (/) or route. For every other path, it will respond with a 404 Not Found.
app.get('/', (req, res) => {
    res.send('Hello World!')
app.listen(port, () => {
    console.log(`Example app listening on port ${port}`)

Steps of running locally
  1. Create a directory named myapp.
  2. cd into the directory and run: npm init.
  3. Command prompts you for a number of things:
    • name: (RETURN for default).
    • version of your application: (RETURN for default).
    • entry point: (default: index.js) app.js
  4. Install express as a dependency (choose one):
    • install Express in the myapp directory and save it in the dependency list: npm install express
    • install Express in the myapp directory temprarily and not add it to the dependency list: npm install express --no-save
  5. Run the app with command: node app.js
  6. Then, load http://localhost:<port>/ in a browser to see the output.

Implement Routing⚓︎

We have already learn Backend Routing. Here, let's see how to implement Routing by using Express.js.

Routing example

Please go to Hoppscotch for implementing POST, PUT and DELETE

const express = require('express');
const bodyParser = require('body-parser');
const app = express();
app.get('/articles', (req, res) => {
  const articles = [];
  // code to retrieve an article...
});'/articles', (req, res) => {
  // code to add a new article...
app.put('/articles/:id', (req, res) => {
  const { id } = req.params;
  // code to update an article...
app.delete('/articles/:id', (req, res) => {
  const { id } = req.params;
  // code to delete an article...
  res.json({ deleted: id });
app.listen(3000, () => console.log('server started'));


Last update: February 27, 2023 00:42:01
Created: December 4, 2022 01:47:38