Express JS For Beginners

PreRequisites

• Basic of Node JS (JavaScript)
• Familiarity with Command Line
• Node installed on linux os

What is express js?

Express JS defined by their official website as:- "It is a minimal and flexible Node.js web application framework that provides a robust set of features for web and mobile applications."

Why Choose Express JS over Other Frameworks?

• Minimal and UnOpinionated
• Middleware Support
• Widely Adopted
• Large Ecosystem
• Active Community

Basic Setup

Create a project folder and initiate node project and create server.js file in that folder.

mkdir demo && cd demo
npm init -y
touch server.js #create server.js file

Install Express & Nodemon packages express for web server and nodemon for reloading the server after each update. so we don't have to start server
manually.

npm i express nodemon

Change scripts in package.json. It will help to reload the server whenever we make changes in file.

...
"scripts":{
    "dev" : "nodemon server.js"
},
...

This is the basic code for the running server that return Hello World! as response on GET: /

server.js

"use strict";
const express = require("express");
const server = express();
const PORT = 8080;

server.get("/", (req, res) => {
  res.send("Hello World!");
});
server.listen(PORT, () => {
  console.log(`On => http://localhost:${PORT}`);
});

To run the sever run the following command on terminal.

npm run dev
# On => http://localhost:8080

Open Browser and type localhost:8080. Hello World! will appear on browser.

Handle Get Route

Creating separate folder and javascript files to handle request like GET, POST, PUT & DELETE.

mkdir -p src/routes src/controllers src/views
touch src/routes/route.js
touch src/controllers/postTodo.js
touch src/views/index.html

Download index.html or paste the html code from here

route.js

const routeHandler = require("express").Router();

routeHandler.get("/todo", (req, res, next) => {
  res.sendFile("./index.html", {
    root: __dirname + "/../views",
  });
});

module.exports = routeHandler;

Router() method called from express js.routeHandler variable now represents an instance of the Express Router, which can be used to define routes and middleware specific to that router. req, res & next parameters are provided by express js to checking request, server response to that request & passing to control to other function, respectively. exporting that as a middleware to the server.

edit server.js

const route = require('./src/routes/route');
server.use(route);

These are some different methods to send response to any request.

// To serve json
res.json({
  success: true,
  message: "Server is working fine",
});

// to send text
res.send("Send some text here");

// redirect to any other page
res.redirect('/)

// don't want to send any response
res.end();

Handle Post Route

The urlencoded middleware is used to parse incoming request bodies with URL-encoded payloads and extended: true help in transforming into json

edit server.js

...
const server = express()

// this will help server to parse json request
server.use(express.json())
server.use(express.urlencoded({ extended: true }));
...

postTodo.js

"use strict";
const postTodo = require("express").Router();

postTodo.post("/todo", (req, res, next) => {
  const data = req.body;
  // validate data
  // save in the data base
  // send res.json({}) data saved successfully
  res.json(req.body);
});

module.exports = postTodo;

req.body contain all data that have been sended to the server.

edit server.js

...
const postTodo = require('./src/controller/postTodo')
server.use(postTodo)
...

Handle PUT & DELETE

Similarly, like GET & POST, we will handle PUT & DELETE.

controllers/updateTodo.js handling PUT request.

"use strict";
const updateTodo = require("express").Router();
updateTodo.put("/todo", (req, res, next) => {
  // validate the data
  // fetch and update the data
  // return res.json({}) that data has been updated
});
module.exports = updateTodo;

controllers/deleteTodo.js handling DELETE request.

"use strict";
const deleteTodo = require("express").Router();
deleteTodo.delete("/todo", (req, res, next) => {
  // validate the data
  // fetch and delete the data
  // return res.json({}) that data has been deleted
});
module.exports = deleteTodo;

Adding Middleware

Middleware is useful library that help us to add some common functionality that we have to need on every web server.
Some popular express js middleware are helmet, body-parser, cookie-parser, jsonwebtoken & many more.

npm i <package_name>

update server.js

...
const packageName = require('packageName')
// check the docs for implementation for that library.
server.use(packageName())
...

Handling 404

Add this code after all routes methods are handled. Because it will block all request and respond that You Lost.

server.use((req, res, next) => {
  res.send("You Lost");
});

You can check out https://expressjs.com/ for more information.

Code

You can download the complete code here.