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Express.js, sometimes referred to as “Express,” stands as the predominant backend framework for Node.js. It is a substantial component within the JavaScript ecosystem, designed to construct single-page, multi-page, and hybrid web applications. Express.js has also emerged as the standard choice for building backend applications with Node.js and serves as the backend component of the MEVN stack.

The MEVN stack, a free and open-source JavaScript software stack for crafting dynamic websites and web applications, includes the following integral elements:

  1. MongoDB: A standard NoSQL database.
  2. Express.js: The default framework for building web applications.
  3. Vue.js: A JavaScript progressive framework used for creating front-end web applications.
  4. Node.js: A JavaScript engine utilized for scalable server-side and networking applications.

This article delves into the essential features of the Express.js framework and provides guidance on constructing your inaugural application with it.

What Is Express.js?

Express.js, sometimes referred to as “Express,” is a minimalist, speedy, Sinatra-like Node.js backend framework. It offers robust features and tools for the development of scalable backend applications. Express.js furnishes a routing system and simplified features, permitting developers to extend the framework with more potent components based on their application’s specific use cases.

Express.js provides an array of tools for web applications, including managing HTTP requests and responses, routing, and middleware, all of which are invaluable for constructing and deploying large-scale, enterprise-ready applications. Additionally, it features a command-line interface tool, the Node Package Manager (NPM), which facilitates the acquisition of developed packages and enforces adherence to the “Don’t Repeat Yourself” (DRY) principle.

The DRY principle aims to minimize the repetition of software patterns, replacing them with abstractions or data normalizations to eliminate redundancy.

What Is Express.js Used For?

Express.js finds application in a wide range of scenarios within the JavaScript and Node.js ecosystem. Developers employ it to create applications, API endpoints, routing systems, and frameworks. Below is a selection of the types of applications that can be constructed using Express.js:

  1. Single-Page Applications: Express.js is an excellent choice for constructing APIs that connect single-page applications, such as Gmail, Google Maps, Airbnb, Netflix, Pinterest, and Paypal.
  2. Real-Time Collaboration Tools: Developers use Express.js to build real-time collaboration and networking applications, simplifying the integration of WebSocket into the framework.
  3. Streaming Applications: Express.js is ideal for constructing complex real-time streaming applications, such as Netflix.
  4. Fintech Applications: With the rising trend in fintech application development, Express.js has emerged as the preferred framework for building highly scalable fintech applications.

Why You Should Use Express.js

Several compelling reasons support the use of Express.js for your next project. It offers faster I/O, a single-thread system, and asynchronous processes. Express.js follows the Model-View-Controller (MVC) structure, streamlining data manipulations and routing systems. Here are some key reasons to consider adopting Express.js:

  1. Flexibility and Speed: Express.js is highly flexible and faster than other Node.js frameworks. It streamlines application development, offering a minimalistic framework with a robust routing system, middlewares, and content negotiation right out of the box.
  2. Part of the MEAN Stack: Express.js is a fundamental part of various stacks, including MERN and MEAN, showcasing its importance in the development process.
  3. Scalability: Express.js has a proven track record of scalability, efficiently handling user requests and responses for large-scale web applications. It boasts excellent modules, packages, and resources to facilitate the creation of reliable and scalable applications.
  4. Supported by Google V8 Engine: Express.js supports multiple Google V8 engine packages, making it a powerful choice for building and deploying real-time, collaborative, and network-based applications at an enterprise level.
  5. Community Support: As the most popular Node.js backend framework, Express.js enjoys extensive community support, resources, and packages to address development challenges. The support from Google further reinforces its popularity among Node.js developers.
  6. Powerful Routing System: Express.js incorporates a robust routing system that assists applications in responding to client requests through specific endpoints. This feature enables developers to create maintainable code by grouping functionalities with the Express router and minimizing repetition.
  7. Middleware: Express.js comprises a series of middleware to enhance the development process, allowing developers to plug in scripts for intercepting the application’s flow. Middleware can be used for tasks such as checking user login status.

How Express.js Works

Express.js operates on the client-server model to handle user requests and deliver responses to clients. Its operation is akin to other popular frameworks like Laravel. When a user sends a request from their web browser, the browser transmits an HTTP request to the application or server, which is often hosted in the cloud.

The server processes the request via one of its routes, utilizing the controller that corresponds to the requested route. After processing, the server sends a response back to the client using HTTP, a communication protocol that facilitates bidirectional communication.

The response can take various forms, including standard text, dynamic HTML pages for rendering web content, or JSON data for presentation on web pages. Below is an example of creating a simple Express.js server to respond to incoming requests:

const express = require('express')
const app = express()
const port = 4000

app.get('/', (request, response) => {
  response.send('Testing Hello World!')
})

app.listen(port, () => {
  console.log(`Test app listening at http://localhost:${port}`)
})

How To Create an Express.js App

To create a practical Express.js application, follow these steps using Express.js 5.0:

  1. Create a directory for your new application and install the required packages:
   mkdir first-express-app
   cd first-express-app
   npm install express@5.0.0-alpha.8 --save
  1. Create an index.js file in the root directory and add the following code:
   const express = require("express");
   const app = express();
   const port = 3000;

   app.listen(port, () => {
     console.log(`Test app listening at http://localhost:${port}`)
   });
  1. Define an array of todos that will be returned to users based on the endpoint called.
   const todos = [
     // List of todos goes here
   ];
  1. Create endpoints for retrieving todos, retrieving a single todo by ID, storing a new todo, updating an existing todo, and deleting a todo. Here’s an example:
   app.get("/todos", (request, response) => {
     response.status(200).json(todos);
   });

   app.get("/todos/:id", (request, response) => {
     response
       .status(200)
       .json({ data: todos.find((todo) => todo.id === request.params.id) });
   });

   app.post("/todos", (request, response) => {
     todos.push(request.body);
     response.status(201).json({ msg: "Todo created successfully" });
   });

   app.put("/todos/:id", (

request, response) => {
     const todo = todos.find((todo) => todo.id === request.params.id);
     if (todo) {
       const { title, desc, completed } = request.body;
       todo.title = title;
       todo.desc = desc;
       todo.completed = completed;
       response.status(200).json({ msg: "Todo updated successfully" });
       return;
     }
     response.status(404).json({ msg: "Todo not found" });
   });

   app.delete("/todos/:id", (request, response) => {
     const todoIndex = todos.findIndex((todo) => (todo.id = request.params.id));
     if (todoIndex) {
       todos.splice(todoIndex, 1);
       response.status(200).json({ msg: "Todo deleted successfully" });
     }
     response.status(404).json({ msg: "Todo not found" });
   });

Testing the Express.js App

To test your Express.js application, run the following command:

node index.js

You can utilize Postman to test your newly developed REST API, ensuring that it returns the expected data. By exploring further and adding more functionality to your application, you can expand your knowledge of Express.js.

Conclusion

Express.js is a powerful and versatile framework for building backend applications in the Node.js ecosystem. Its flexibility, speed, scalability, and robust community support make it a top choice for developers. By following the steps provided in this guide, you can create your own Express.js applications and harness the framework’s capabilities for various use cases.