Node.js Exam Notes PDF

Node.js Exam Notes Overview of Node.js Definition: Node.js is a JavaScript runtime built on Chrome’s V8 engine, designed for developing server-side and network applications. Features: Event-driven, non-blocking I/O model for efficient, real-time, data-intensive...

Node.js Exam Notes Overview of Node.js Definition: Node.js is a JavaScript runtime built on Chrome’s V8 engine, designed for developing server-side and network applications. Features: Event-driven, non-blocking I/O model for efficient, real-time, data-intensive applications. Runs on a single-threaded event loop, handling asynchronous tasks in the background, ensuring scalability. Node.js Modules Module System: Each JavaScript file is a separate module. Types of Modules: Core/Built-in Modules: Pre-installed with Node.js (e.g., file system, networking). Local Modules: User-defined modules in the project directory. Third-Party Modules: Installed via NPM (Node Package Manager), either globally or locally. Importing Modules: Use the require() function. Localhost Definition: Refers to the local machine or loopback address (127.0.0.1). Purpose: Used for testing web applications during development before deployment. Client-Server Protocol Communication Process:  1. Connection Establishment: Client connects to the server (via TCP). 2. Request/Response: Client sends a request; server responds. 3. Session Phases: Request sent. Server processes request. Response returned with status code and data. Express.js Overview Definition: Express.js is a third-party framework for Node.js, known for simplicity and flexibility. Key Features: Routing: Manages HTTP requests and responses. Static File Serving: Serves files like HTML, CSS, and JS. Error Handling: Customizes error responses. Database Integration: Connects to databases (e.g., MongoDB, MySQL). Session Management: Manages user sessions. Request/Response Handling: Processes requests and sends responses. MEAN Stack: Part of the MEAN stack (MongoDB, Express.js, Angular, Node.js) for dynamic web apps. Express.js Routing Routing: Defines server responses to HTTP requests via URL paths and methods (e.g., GET, POST). Route Handlers: Functions that process requests for matched routes. Middleware: Functions executed sequentially before final request handlers for tasks like authentication or error handling. Handling Requests and Responses Request Object (req): Contains client request details (headers, body, query parameters). Response Object (res): Sends responses to the client (status codes, JSON data). Error Handling in Express.js Error Handling Middleware: Centralized error control for consistent responses. Ensures robustness by managing unexpected scenarios gracefully. Setting Up the Server: Use app.listen() for quick and efficient server setup. Overview of NoSQL Databases Definition: “Not Only SQL,” designed for unstructured/semi-structured data. Characteristics: Non-relational: No fixed schemas. Distributed: Data spread across multiple machines. Open-source: Often free to use. Horizontally Scalable: Scaled by adding servers. ACID Properties in NoSQL Atomic: Transactions are fully completed or rolled back. Consistent: Adheres to defined rules after a transaction. Isolated: Transactions run without interference. Durable: Changes persist despite failures. CAP Theorem (Consistency, Availability, Partition Tolerance)  Basic Availability: Guaranteed response, even if inconsistent. Soft-state: Data changes over time without input. Eventual Consistency: Synchronization achieved eventually. Types of NoSQL Databases Key-Value Stores: Key-value pairs (e.g., Redis). Document-Based: Semi-structured data (e.g., MongoDB). Column-Based: Columnar data storage (e.g., Cassandra). Graph-Based: Nodes and edges for relationships (e.g., Neo4j). MongoDB Key Concepts Structure: Databases: Store collections of documents. Collections: Groups of related documents. Documents: Individual records in BSON format. Unique Identifier: _id field automatically assigned as primary key. Collection Creation: Automatic: Created when inserting the first document. Explicit: Use db.createCollection("name"). MongoDB Update Methods Update Parameters: Query: Conditions to locate documents. Fields: Data to update, add, remove, or rename. Options: Additional behaviors (e.g., upsert). Compound Operators:  AND: Implicit for multiple conditions. OR: Use $or or $in for flexibility. Mongoose is an Object Data Modeling (ODM) library for MongoDB in Node.js, designed to simplify interactions with MongoDB. It enables developers to: Define schemas for structured data. Manage data relationships. Validate data before saving. Key Components Schema: Blueprint defining the structure, types, and validations for documents in a MongoDB collection. Model Provides methods to perform CRUD operations on documents using the defined schema. Middleware: Logic applied during pre- and post-processing stages, such as validations or transformations. Plugins :Extend Mongoose functionality, adding features like timestamps or custom validations. Mongoose Workflow Install and import the Mongoose module. Define a Schema: Outline the document structure and data types. Create a Model: Represents the MongoDB collection and provides CRUD methods. Connect to the database: Establish a connection to the MongoDB instance.