Express.js is a popular web application framework for Node.js. It simplifies the process of building web applications and APIs by providing a set of features and abstractions for handling common web development tasks. This explanation will cover some of the key concepts and features of Express.js, with examples and code snippets from the project located at https://github.com/benhall/express-demo/.
The Big Picture
Express.js is a minimal and flexible Node.js web application framework that provides a robust set of features for web and mobile applications. It is designed to be easy to use and customizable, with a focus on performance and scalability. Express.js is often used in conjunction with other libraries and tools, such as Handlebars, Cookie-parser, Morgan, Debug, Http-errors, Docker, Node.js, and Nodemon.
Design Philosophy
Express.js follows the Node.js philosophy of “small, fast, and opinionated.” It is designed to be unobtrusive and modular, allowing developers to choose the features and libraries they need for their specific project. Express.js is also designed to be easy to learn and use, with a clear and consistent API.
Programming Languages
Express.js is written in JavaScript, which is a popular and widely-used programming language for web development. JavaScript is a dynamic, interpreted language that is well-suited for building web applications and APIs.
Express.js
Express.js is a Node.js web application framework that provides a robust set of features for web and mobile applications. It is designed to be easy to use and customizable, with a focus on performance and scalability. Express.js provides a simple and intuitive API for handling common web development tasks, such as routing, middleware, and template rendering.
Here is an example of how to create a basic Express.js server:
const express = require('express');
const app = express();
app.get('/', (req, res) => {
res.send('Hello, world!');
});
app.listen(3000, () => {
console.log('Express server listening on port 3000');
});
This code creates an Express.js server that listens on port 3000 and responds with “Hello, world!” when a GET request is made to the root URL (“/”).
Handlebars
Handlebars is a popular templating engine for Node.js and Express.js. It allows developers to create dynamic and reusable templates for their web applications. Handlebars is designed to be simple and easy to use, with a clear and consistent syntax.
Here is an example of how to use Handlebars with Express.js:
const express = require('express');
const exphbs = require('express-handlebars');
const app = express();
app.engine('handlebars', exphbs());
app.set('view engine', 'handlebars');
app.get('/', (req, res) => {
res.render('home', {
title: 'Welcome to my website',
message: 'Thank you for visiting!'
});
});
app.listen(3000, () => {
console.log('Express server listening on port 3000');
});
This code creates an Express.js server that uses Handlebars as its template engine. It defines a route for the root URL (“/”) that renders a template called “home” with the variables title and message.
Cookie-parser
Cookie-parser is a middleware for Express.js that parses incoming cookies and makes them available on the req.cookies object. This is useful for storing and retrieving small amounts of data, such as user preferences or session IDs.
Here is an example of how to use cookie-parser with Express.js:
const express = require('express');
const cookieParser = require('cookie-parser');
const app = express();
app.use(cookieParser());
app.get('/', (req, res) => {
res.cookie('name', 'John Doe');
res.send('Cookie set!');
});
app.get('/read-cookie', (req, res) => {
const name = req.cookies.name;
res.send(`Hello, ${name}!`);
});
app.listen(3000, () => {
console.log('Express server listening on port 3000');
});
This code creates an Express.js server that uses cookie-parser to parse incoming cookies. It defines two routes: one that sets a cookie with the name “name” and a value of “John Doe”, and another that reads the cookie and sends a personalized greeting.
Morgan
Morgan is a middleware for Express.js that logs incoming requests and responses. It provides a simple and flexible way to track and debug your web application.
Here is an example of how to use Morgan with Express.js:
const express = require('express');
const morgan = require('morgan');
const app = express();
app.use(morgan('dev'));
app.get('/', (req, res) => {
res.send('Hello, world!');
});
app.listen(3000, () => {
console.log('Express server listening on port 3000');
});
This code creates an Express.js server that uses Morgan to log incoming requests and responses. It sets the log format to “dev”, which provides detailed information about each request.
Debug
Debug is a Node.js library for debugging Node.js applications. It provides a simple and flexible way to log messages and inspect variables at runtime.
Here is an example of how to use Debug with Express.js:
const express = require('express');
const debug = require('debug')('app');
const app = express();
app.get('/', (req, res) => {
debug('Received request for root URL');
res.send('Hello, world!');
});
app.listen(3000, () => {
console.log('Express server listening on port 3000');
});
This code creates an Express.js server that uses Debug to log messages. It sets the log prefix to “app”, which will be included in each log message.
Http-errors
Http-errors is a Node.js library for creating and handling HTTP errors. It provides a simple and consistent way to create and respond to HTTP errors, such as 404 Not Found or 500 Internal Server Error.
Here is an example of how to use Http-errors with Express.js:
const express = require('express');
const httpErrors = require('http-errors');
const app = express();
app.get('/user/:id', (req, res, next) => {
const id = req.params.id;
if (id === '123') {
res.send('User 123 found');
} else {
next(httpErrors(404, 'User not found'));
}
});
app.use((err, req, res, next) => {
res.status(err.status || 500);
res.send(err.message);
});
app.listen(3000, () => {
console.log('Express server listening on port 3000');
});
This code creates an Express.js server that uses Http-errors to handle HTTP errors. It defines a route for the URL “/user/:id” that looks for a user with the specified ID. If the user is found, it sends a response with the message “User 123 found”. If the user is not found, it calls the next function with an Http-errors instance, which will generate a 404 Not Found response.
Docker
Docker is a popular containerization platform for Node.js applications. It allows developers to package their applications and dependencies into a single, self-contained unit that can be deployed and run on any system.
Here is an example of how to use Docker with Express.js:
# Dockerfile
FROM node:14
WORKDIR /app
COPY package*.json ./
RUN npm install
COPY . .
EXPOSE 3000
CMD ["npm", "start"]
This Dockerfile creates a Node.js container that runs the Express.js server. It installs the dependencies, copies the application code, and exposes port 3000 for incoming requests.
Node.js
Node.js is a JavaScript runtime environment for building server-side applications. It is built on the V8 JavaScript engine
