Node.js & Express.js: Modules, Routing, REST APIs, and JSON

Posted on Apr 1, 2025 in Computers

Node.js Modules

Modules in Node.js are reusable code blocks that organize functionality into smaller, manageable files. Each module can export functions, objects, or values for other files to import and use.

Types of Modules

  • Core Modules: Built into Node.js, requiring no installation.
  • Local Modules: Created by developers for specific tasks.
  • Third-Party Modules: Installed using npm (Node Package Manager).

Core Modules

Core modules provide essential functionalities like file handling, HTTP requests, and path management. Key examples include:

  • HTTP Module: Creates web servers and handles requests/responses.
  • FS (File System) Module: Reads and writes files.
  • Path Module: Manages file paths.
  • Events Module: Handles event-driven programming.

Example: When building a web server, the http module enables server creation and request handling without external dependencies, making Node.js efficient for scalable applications.

Express.js Routing

Routing in Express.js determines how the server responds to client requests at various endpoints (URIs). Each route associates with an HTTP method (GET, POST, PUT, DELETE) and a path, defining request handling.

Route Examples

  • Home Route: Displays the homepage.
  • About Route: Provides app information.
  • Contact Route: Handles inquiries.

Routing is crucial for building APIs or web apps. It organizes requests, directs them to appropriate handlers, and enhances code structure and readability.

Body Parser Module

Body Parser is Express.js middleware that parses incoming request bodies before they reach route handlers. Clients often send data via forms or JSON payloads, which Node.js doesn’t handle automatically. Body Parser addresses this.

Benefits

  • Parses incoming JSON, making data accessible via req.body.
  • Handles URL-encoded data, simplifying form submissions.
  • Simplifies handling POST request data.

Example: In login forms, Body Parser extracts submitted email and password, making them available as req.body.email and req.body.password for direct use.

REST APIs

A REST API (Representational State Transfer API) is a rule set enabling web communication between applications using HTTP. REST APIs employ a stateless architecture, requiring each request to contain all necessary information without server-side session storage.

Key REST Characteristics

  • Stateless: No server-side sessions; each request is independent.
  • Client-Server: Separates client-side UI and server-side data processing.
  • Cacheable: Responses can be cached for performance.
  • Uniform Interface: Standardized methods for resource actions.

Common HTTP Methods

  • GET: Retrieves data (e.g., fetching books from /books).
  • POST: Creates new resources (e.g., adding a book to /books).
  • PUT: Fully updates resources (e.g., updating book details at /books/:id).
  • PATCH: Partially updates resources (e.g., updating book title at /books/:id).
  • DELETE: Removes resources (e.g., deleting a book at /books/:id).

REST APIs promote modularity, reusability, and scalability through clearly defined resource actions.

JSON and JSON Parsing

JSON (JavaScript Object Notation) is a lightweight data format for server-client data exchange. It’s human and machine-readable, using key-value pairs.

JSON Example

{
  "name": "John Doe",
  "age": 30,
  "isStudent": false,
  "courses": ["Math", "Science", "History"]
}

JSON Parsing

JSON parsing converts JSON data into a programming language-usable format (e.g., JSON strings to JavaScript objects or Python dictionaries).

  • JavaScript: JSON.parse() converts JSON strings to objects.
  • Python: json.loads() parses JSON strings into dictionaries.

Parsing enables applications to access and manipulate data from APIs or files, essential for modern web development.