NODE JS - NPM

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 1) What is NPM?

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- Node Js npm (Node Package Manager) is a package manager for JavaScript, which is used for managing dependencies in Node.js applications.

- With npm, we can easily install, manage, and update packages (Libraries/ Modules) that you can use in your applications.

- www.npmjs.com hosts thousands of packages to download and use

- To install a package using npm - 

npm install package-name

   This will download the package and add it to your node_modules directory, along with dependencies.

- Example - 

                    To install Express, you can run the below command - 

  npm install express

or
npm i express

- Always include the installed package in your package.json file by adding them to the dependencies section.

Click Here to Learn about the Asynchronous Programming 

NODE JS BUILT-IN MODULE - FS

 1) What does FS module do?

1) The Node fs module provides functions for interacting with the file system on your computer.

2) It allows you to perform various operations such as reading from and writing to the files, creating and deleting files/folders, and much more.

3) Importing the 'fs' module:

var fs = require('fs');

Examples of various operations are below:

2) Reading from a file

fs.readFile('example.txt', 'utf8', (err, data) => {          if (err) {                  console.error(err);                  return;                  }          console.log(data);  });

3) Creating a new file

There are three ways to create a new file using the fs module-

1) Using appendFile() method -  This method appends specified content to a file. If the file does not exist, a new file will be created.

fs.appendFile('mynewfile1.txt', 'Hello content!', function (err) {          if (err)                  throw err;          console.log('Saved!');  });

2) Using the open() method - This method opens the specified file for writing if the flag (second argument) is passed as w which means writing. If the file does not exist, a new file will be created.

fs.open('mynewfile2.txt', 'w', function (err, file) {          if (err)                  throw err;          console.log('Saved!');  });

3) Using the writeFile() method - This method replaces the specified file and content if it exists. If the file does not exist, a new file will be created.

fs.writeFile('mynewfile3.txt', 'Hello content!', function (err) {          if (err)                  throw err;          console.log('Saved!');  });

4) Deleting a File

The fs.unlink() method deletes the specified file.

fs.unlink('myfile.txt', function (err) {          if (err)                  throw err;          console.log('File deleted!');  });

Click Here to Learn about the Node JS NPM 

NODE JS BUILT IN MODULE - URL

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1) What does the URL Module do? 

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1) Node JS 'url' module provides utilities for URL resolution and parsing.

2) It allows you to parse URLs into their components (such as protocol, hostname, port, path, hash, query parameters, and more) and format URL strings from these components.

3) To import the URL module in your application, use the require() method:

    var url = require ('url');

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2) URL Parse() method

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url.parse() method can parse the address and returns a URL object with each part of the address as properties.

Example:

const url = require('url');  const urlString = 'https://example.com:8080/path?query=value';  const parsedUrl = url.parse(urlString, true);  // Pass true as the second argument to parse query parameters  console.log(parsedUrl);

We can also print the hostname, pathname, and query as well- 

console.log (parsedUrl.host); // returns example.com:8080

console.log (parsedUrl.pathname); // returns /path

console.log (parsedUrl.search); // returns ?query=value

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3) URL Resolve() method

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The url.resolve() method resolves a relative URL path against a base URL.

Example:

const url = require('url');  const baseUrl = 'https://example.com/users';  const relativePath = '/profile';  const resolvedUrl = url.resolve(baseUrl, relativePath);  console.log(resolvedUrl);  // returns https://example.com/profile

Click Here to Learn about the Built-in Module - FS

NODE JS BUILT IN MODULE - HTTP

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1) Creating an HTTP Server

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1) We need to first import the 'http' module using the require function
                            var http = require ('http');

2) We will use the method createServer() to create an HTTP server:
                            http.createServer(function (req, res){

                            ... // your code here

                            }).listen(PORT_NUMBER); 

Example: 

// Import the built-in 'http' module  const http = require('http');  // Define the hostname and port number  const hostname = '127.0.0.1';  const port = 3000;  // Create an HTTP server  const server = http.createServer((req, res) => {          // Set the HTTP status code and content type in the response header          res.writeHead(200, {'Content-Type': 'text/plain'});          // Send the response body          res.end('Hello, world!\n');          });           // Start the server and listen on the specified port and hostname  server.listen(port, hostname, () => {         console.log(`Server running at http://${hostname}:${port}/`);  });

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2) GET REQUEST to query

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1) We will be using http.request() method to send an HTTP GET request to a server and handle the response.

2) Similarly, we will be importing the module using- 

                            var http = require ('http');

3) We will be defining the options for the HTTP request where we will be mentioning the hostname, port number, path (if any), and the method.

                            const options = {

                            hostname: 'jsonplaceholder.typicode.com',

                            port: 80,

                            path: '/posts',

                            method: 'GET'

                            }

4) Creating a http.request() method in which we are going to pass the above options object.

5) Store the response and display it or process it when the response is complete.

Example: 

// Import the built-in 'http' module  const http = require('http');  // Define the options for the HTTP request  const options = {          hostname: 'jsonplaceholder.typicode.com',          port: 80,          path: '/posts',          method: 'GET' }; // Create the HTTP request  const req = http.request(options, (res) => {          // Initialize a variable to store the response data          let data = '';          // Concatenate chunks of data as they are received          res.on('data', (chunk) => {                  data += chunk;          });           // When the response is complete, log the data to the console          res.on('end', () => {              console.log(data);          });  });  // Handle errors that occur during the request  req.on('error', (error) => {          console.error('An error occurred:', error);  });  // End the request  req.end();

Click Here to Learn about the Built-in Module - URL

MODULES IN NODE JS

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 1) Modules in Node Js

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1) In Node Js, modules are reusable blocks of code that encapsulate related functionality.

2) Modules allow you to organize your code into separate files and directories, making it easier to manage and maintain your projects.

3) We can define modules in separate files and then import and use them in other files using the 'require()' function (User-Defined Modules).

4) There are two types of modules - User-Defined Modules and Predefined Modules (Built-in Modules) 

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1.1) What are User-Defined Modules?

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Definition - User-defined modules are created by the developers to encapsulate and reuse the code across their own applications. These modules are typically stored in separate files within the applications's directory.

Developers can create their own modules and export them using the "module.exports".
The same modules can be imported and used in other parts of the application using the "require()" function.

Example: myFirstModule.js

function greetWithPersonName(name) {         console.log ( `Hello ${name}! `);              //Here we have used the tilde operator } module.exports = greetWithPersonName;

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1.2) What are Predefined Modules/ Built-in Modules/ Core Modules?

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Definition: Predefined modules are provided by Node.js itself and are available for use without the need for installation. These modules are part of the Node.js runtime environment and provide various functionalities for common tasks such as file system operations, networking, HTTP, and more.

Developers can use the predefined modules by importing and using them in Node.js applications in the same way as user-defined modules, using the require() function.

Example: usePreDefMod.js

// We are going to use a file system module to manage the file 

const fs = require ('fs'); fs.readFile ('text.txt, 'utf8', (err, data) => {         if (err) {             console.error (err);             return;         }         console.log (data); });

Click Here to Learn about Built-in Module - HTTP

NODE JS INTRODUCTION

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1) What is Node Js?

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- Node Js is an open-source server environment that runs on various platforms like Windows, Linux, Unix, Mac OS, etc.

- Node Js is a runtime environment that allows you to run JavaScript code on the server side.

- Node Js uses the V8 Javascript engine.

- Node Js is commonly used to build scalable network applications because of its event-driven, non-blocking I/O model, which makes it efficient and lightweight.

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2) Why to use Node Js?

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- Javascript can be used for Server-side and Client-side development (Frontend and Backend of an application).

- Node Js is an event-driven, non-blocking I/O model, which makes it efficient and scalable for handling concurrent connections. Node Js can handle multiple requests without getting blocked (Useful for real-time applications).

- V8 Javascript engine compiles JavaScript directly into machine code before executing it (High Performance).

- Since Node Js is non-blocking, and has event-driven architecture, it is inherently scalable (Can easily handle many concurrent connections).

- Plenty of resources and support available for developers who are using Node Js (Documentation, Tutorial, and more)

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3) How to download Node Js?

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- Node js can easily be installed from the official site - https://nodejs.org/en

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4) Writing the first Node Js program.

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// Import the built-in 'http' module const http = require('http'); // Create an HTTP server that listens on port 5000 const server = http.createServer((req, res) => {      // Set the response HTTP header with HTTP status and content type      res.writeHead(200, {'Content-Type': 'text/plain'});     // Write the response body ("Hello, world!")     res.end('Hello World!!'); }); // Start the server and listen on port 5000 server.listen(5000, () => {     console.log('Server is now running at http://localhost:5000/'); });

To run this code on your local machine:-

1) Copy and paste the above code into the file - helloworld.js

2) Open the command prompt and navigate to the folder where helloworld.js is saved

3) Run the command node helloworld.js

4) You should see the message "Server is now running at http://localhost:5000/"

5) Open any web browser and navigate to http://localhost:5000/ and you will see Hello World!!

Click Here to Learn Modules in Node Js

C program that uses a loop to calculate the factorial of a given number

// Factorial program using function

#include <stdio.h>

// Function prototype

long long calculateFactorial(int n);

int main() {

    int number;
    // Get input from the user

    printf("Enter a non-negative integer: ");
    scanf("%d", &number);

    // Check if the input is non-negative

    if (number < 0) {
        printf("Please enter a non-negative integer.\n");
        return 1; // Return with an error code
   }

    // Calculate and display the factorial using a loop

    long long factorial = calculateFactorial(number);
    printf("Factorial of %d = %lld\n", number, factorial);
    return 0;

}

// Function to calculate factorial using a loop

long long calculateFactorial(int n) {
    if (n == 0 || n == 1) {
        return 1;
    } else {
         long long result = 1;
        for (int i = 2; i <= n; ++i) {
           result *= i;
        }
        return result;
    }
}

C program example that uses functions - This program calculates the sum of two numbers using separate functions for input, addition, and output.

#include <stdio.h>

// Function prototypes
    int getInput();
    int addNumbers(int num1, int num2);
    void displayResult(int result);

int main() {
    // Get input from the user
    int number1 = getInput();
    int number2 = getInput();

    // Perform addition
    int sum = addNumbers(number1, number2);

    // Display the result
    displayResult(sum);
    return 0;
}

// Function to get input from the user
    int getInput() {
    int num;
    printf("Enter a number: ");
    scanf("%d", &num);
    return num;
}

// Function to add two numbers
    int addNumbers(int num1, int num2) {
    return num1 + num2;
}

// Function to display the result
    void displayResult(int result) {
    printf("The sum is: %d\n", result);
}

Node js program - IF ELSE IF example

# Node js program using if else if statement

var a = 'route 1';

if (a === 'route 1'){
    console.log ('Route is 1');
}else if ( a === 'route 2')  {
     console.log ('Route is 2');
}else {
    console.log ( 'No Route');
}

## When you run this program

## Output will be - 

Route is 1