Nodejs Modules:

         Node.js modules are reusable blocks of code that encapsulate related functionalities.

They help in organizing and managing code by dividing it into separate files, each serving a specific purpose.

Node.js supports both built-in core modules and user-defined custom modules.

Types of Modules:

 

Core:

• These are built into Node.js and can be used without installing any additional packages.
• Examples include fs (file system operations), http (HTTP server and client), path (file and directory path utilities), and os (operating system utilities).
• Syntax : const module = require('module_name');

 

 

 

 

Types of Core Modules:

S. No	Types	Definition
1	File System	Provides an API for interacting with the file system, allowing you to read, write, delete, and manage files and directories.
2	HTTP	Used to create HTTP servers and clients, enabling you to build web servers and make HTTP requests.
3	Path	Provides utilities for working with file and directory paths.
4	OS	Provides information about the operating system and utilities related to it.
5	Util	Provides utility functions that are helpful for debugging and various common tasks.
6	Events	Provides an implementation of the event-driven architecture, allowing you to create and handle custom events.
7	Stream	Provides an API for working with streaming data, such as reading from or writing to files, network communications, or any kind of end-to-end information exchange.
8	Crypto	Provides cryptographic functionalities to handle encryption, decryption, and hashing.
9	Buffer	Provides a way to handle binary data directly in memory, especially useful for working with streams of data.

 

Local:

• These are custom modules created by the user to organize and modularize their own code.
• Local modules can be files or directories containing multiple files.

Third Party:

• These are modules created by the community and shared via the Node Package Manager (NPM).
• Examples include express (web framework), lodash (utility library), and mongoose (MongoDB object modeling).

Installation:

• Third-party modules are installed via NPM.
• Installation can be global (available to all projects) or local (specific to a project).

 

 

Global Objects:

         Node.js global objects are available in all modules and do not require an import to be used. They provide a variety of useful functionalities and are part of the core Node.js API. Here are some of the most commonly used global objects and functions:

1. global

Description: global is the global namespace object in Node.js. Any property attached to global becomes available globally across all modules.

Example:

2. process

Description: The process object provides information about the current Node.js process. It allows interaction with the runtime environment, including standard input/output, environment variables, and command-line arguments.

Common Properties and Methods:

process.env: Environment variables.

process.argv: Command-line arguments.

process.exit(): Exits the process.

process.on(event, callback): Listens for process events like 'exit', 'uncaughtException', etc.

 

3. console

Description: The console object provides a simple debugging console that is similar to the JavaScript console provided by web browsers.

Common Methods:

console.log(): Prints to stdout.

console.error(): Prints to stderr.

console.warn(): Prints a warning message to stderr.

console.info(): Prints informational messages to stdout.

Example:

 

 4. Buffer

Description: The Buffer class is used to handle binary data directly in Node.js. It is especially useful for working with streams and file I/O.

Common Methods:

Buffer.from(): Creates a new buffer from a string, array, or another buffer.

buf.toString(): Converts the buffer to a string.

buf.write(): Writes data to the buffer.

Example:

5. setImmediate(callback)

Description: setImmediate schedules a callback to execute after the current event loop tick. It is similar to setTimeout but with no delay.

Example:

6. setInterval(callback, delay)

Description: setInterval repeatedly calls the provided callback function with a fixed time delay between each call.

Example:

7. setTimeout(callback, delay)

Description: setTimeout schedules a callback to be executed after a specified delay in milliseconds.

Example:

8. __dirname and __filename

Description: __dirname is the directory name of the current module. __filename is the file name of the current module.

Example:

File System Operation:

         Node.js provides a powerful set of tools for file system operations through its fs (file system) module. Below are some common operations you can perform with this module, including

1. reading,
2. writing,
3. updating,
4. deleting files,
5. directories.

Import the fs module:

 

In Node.js, synchronous and asynchronous approaches to file system operations refer to different ways of handling tasks, especially in terms of how they affect the execution flow of your program. Here’s an overview of each approach:

Synchronous Approach

Definition:

Synchronous operations block the execution of the program until the operation completes. This means the program waits for the task to finish before moving on to the next line of code.

 

 

Characteristics:

Blocking: The entire program execution is paused until the synchronous operation completes.

Simple to Understand: The code execution flow is straightforward and sequential.

Potentially Inefficient: Can lead to performance bottlenecks, especially in I/O operations like file reading/writing, because other operations cannot proceed while waiting.

Example:

Asynchronous Approach

Definition: Asynchronous operations allow the program to continue executing the next line of code while the operation completes in the background. A callback, promise, or async/await is used to handle the completion of the operation.

Characteristics

Non-blocking: The program continues executing other code without waiting for the operation to complete.

Efficient: Improves performance and responsiveness, especially in I/O-bound operations.

Complexity: Managing the execution flow can be more complex due to callbacks, promises, or async/await.

Example:

Reading Files:

Asynchronously:

         In this example, fs.readFile reads the content of a file. The operation is non-blocking, and a callback function is invoked when the reading is complete. If there's an error (e.g., the file doesn't exist), it will be passed to the err parameter.

Synchronously:

Here, fs.readFileSync reads the file content in a blocking manner. The program will wait until the file has been read before proceeding.

 

Writing Files:

Asynchronously

fs.writeFile writes data to a file, replacing the file if it already exists. The operation is non-blocking, and the callback is invoked once the write operation is complete.

Synchronously

 fs.writeFileSync performs the write operation in a blocking manner. The program execution is paused until the write is complete.

 

Appending to Files

Asynchronously

fs.appendFile adds data to the end of a file. The operation is non-blocking, and a callback is invoked once the append operation is complete.

Synchronously

fs.appendFileSync performs the append operation in a blocking manner.

Closing Files

In Node.js, you usually don't need to manually close files when using high-level file operations like readFile or writeFile. However, when working with lower-level file descriptors, you need to close files using fs.close.

 

Example with File Descriptors

In this example, fs.open opens a file and provides a file descriptor (fd). After performing some operations, fs.close is used to close the file.

Deleting Files:

Asynchronously

fs.unlink deletes a file. The operation is non-blocking, and the callback is invoked once the delete operation is complete.

Synchronously

 

fs.unlinkSync performs the delete operation in a blocking manner.

 

 

 

 

 

 

 

Event Driven Programming:

         Event-driven programming is a programming paradigm in which the flow of the program is determined by events, such as user actions (clicks, key presses), sensor outputs, or messages from other programs/threads.

Events and Events Emitters:

1. Events: These are signals that something has happened, such as a user action or a message from another process.
2. Event Emitters: In Node.js, objects that emit events are instances of the EventEmitter class. These objects expose an interface for binding event listeners and emitting events.

Event Loop:

The event loop is a core concept in Node.js. It allows Node.js to perform non-blocking I/O operations by offloading operations to the system kernel whenever possible.

EventEmitter Class:

The EventEmitter class is a central part of Node.js' event-driven architecture. It provides methods to emit and listen for events. Here is an example of how to use it:

 

 

 

Example:

1. Efficient Asynchronous Handling:

Allows for non-blocking operations, making it possible to handle multiple tasks simultaneously without waiting for one to complete before starting another.

1. Improved Scalability:

Handles numerous concurrent connections efficiently, making it ideal for web servers and real-time applications that require high concurrency.

1. Simplified Code Structure:

Enables modular and decoupled code, as different parts of the program can respond to events independently. This leads to cleaner and more maintainable code.

 

 

 

1. Responsive Applications:

Enhances responsiveness by immediately reacting to user inputs or other events, improving the user experience in interactive applications.

1. Resource Efficiency:

Reduces the need for creating multiple threads, thus saving memory and CPU resources, which is particularly beneficial in resource-constrained environments.

1. Flexibility and Adaptability:

Easily integrates with various I/O operations, such as file systems, network requests, and databases, providing a versatile foundation for building a wide range of applications.

Disadvantages:

1. Complexity in Managing State:

Keeping track of the application state can become challenging as the application grows, especially when handling many events that can occur in various orders.

1. Callback Hell:

When multiple asynchronous operations are nested within each other, it can lead to deeply nested callbacks, making the code difficult to read and maintain. This is often referred to as "callback hell."

 

 

1. Error Handling:

Handling errors in an event-driven architecture can be more complex. Errors need to be caught and handled correctly within event handlers, and missed errors can propagate silently, making debugging difficult.

1. Memory Leaks:

If event listeners are not properly removed, they can cause memory leaks by holding references to objects that are no longer needed.

1. Testing and Debugging:

Writing tests for event-driven code can be challenging due to the asynchronous nature of events. Debugging can also be harder since the flow of execution is not linear.

1. Performance Overhead:

There can be a performance overhead associated with the event loop and the context switching between different event handlers.

 

HTTP and Web Servers in Node.js

         Node.js provides built-in modules to create and manage web servers. The primary module for handling HTTP requests and responses is the http module. This module allows you to create a web server that can listen for and respond to HTTP requests.

1. HTTP Module: The core module for creating HTTP servers and handling HTTP requests and responses.
2. Request Object: Represents the incoming HTTP request. Contains details such as the request method, URL, headers, and body.
3. Response Object: Represents the outgoing HTTP response. Allows you to set the status code, headers, and body content of the response.

Example:

         Here’s a simple example of how to create an HTTP server in Node.js that listens on a specified port and responds with a "Hello, World!" message.

Step-by-Step Guide

Initialize a Node.js Project:

If you haven’t already, create a new directory for your project and initialize a Node.js project.

 

Create the Server File:

Create a file named server.js and add the following code:

Run the Server:

In your terminal, navigate to the project directory and run the server using Node.js.

Access the Server:

Open your web browser and navigate to http://127.0.0.1:3000. You should see the message "Hello, World!".

 

 

 

Asynchronous Programming:

Asynchronous programming in Node.js is a key feature that allows the handling of multiple tasks simultaneously without blocking the execution of other operations. This model is essential for handling I/O-bound operations, such as reading from files, making HTTP requests, or querying databases, efficiently. Here's a comprehensive overview of asynchronous programming in Node.js:

1. Event Loop

Node.js uses a single-threaded event loop architecture to handle asynchronous operations. The event loop continually checks for completed tasks and executes their callbacks. This non-blocking I/O model enables Node.js to manage thousands of connections concurrently.

2. Callback Functions

Callbacks are the simplest form of handling asynchronous operations. A callback function is passed as an argument to another function, which executes the callback once the operation is complete.

 

3. Promises

Promises provide a cleaner way to handle asynchronous operations compared to callbacks. A Promise represents an operation that will complete in the future, producing a value or an error.

4. Async/Await

Async/Await, introduced in ES2017, simplifies the syntax for working with Promises. It allows writing asynchronous code that looks synchronous, improving readability and maintainability.

5. Event Emitters

Event Emitters are objects in Node.js that emit named events and allow functions (event listeners) to subscribe to those events. The EventEmitter class is central to many of Node.js’s core modules.

6. Timers

Node.js provides several functions to execute code after a delay or at regular intervals, such as setTimeout, setInterval, and setImmediate.

7. Streams

Streams are another core concept in Node.js for handling I/O operations efficiently. Streams allow reading or writing data piece by piece, rather than all at once, which is useful for large files or data.

 

 8. Using Libraries

Many Node.js libraries and frameworks, such as Express.js for web development, are designed with asynchronous programming in mind. These libraries often provide built-in support for Promises and async/await.