# Day 2: Understanding Core Modules and the Event Loop: Using Modules and npm Node.js core modules (e.g., fs, path, http, os) Understanding the Event Loop Synchronous vs Asynchronous programming in Node.js Practical: Basic file operations using fs module (read, write, append) Handling paths with path module Timing events with setTimeout and setInterval #### **Event Loop in Node.js** **What is the Event Loop?** * Node.js uses an **event-driven, non-blocking I/O model** which makes it lightweight and efficient. The **event loop** is responsible for handling asynchronous operations. It allows Node.js to handle multiple operations without creating multiple threads. **Example of Event Loop:** ```javascript console.log('Start'); setTimeout(() => { console.log('Timeout function executed'); }, 2000); console.log('End'); ``` #### **Synchronous vs Asynchronous Programming** * **Synchronous**: * Operations that block further code execution until the current task is finished. In Node.js, most operations can be done asynchronously to avoid blocking the event loop. **Example of Synchronous Code:** ```javascript const fs = require('fs'); console.log('Start reading file...'); const data = fs.readFileSync('example.txt', 'utf-8'); console.log(data); console.log('Finished reading file.'); ``` * This code **blocks** further execution until the file is completely read. * **Asynchronous**: * Non-blocking operations that allow the rest of the program to run while waiting for a task (like reading a file) to complete. **Example of Asynchronous Code:** ```javascript const fs = require('fs'); console.log('Start reading file...'); fs.readFile('example.txt', 'utf-8', (err, data) => { if (err) throw err; console.log(data); }); console.log('Finished reading file.'); ``` * Here, Node.js will continue executing other code (e.g., "Finished reading file.") while waiting for the file to be read. * ### **2\. Practical:** --- #### **Basic File Operations with** `fs` Module * **fs (File System) module:** * Allows working with the file system, such as reading, writing, and appending to files. * **Reading a File (Asynchronous):** ```javascript const fs = require('fs'); fs.readFile('example.txt', 'utf-8', (err, data) => { if (err) throw err; console.log('File contents:', data); }); ``` * **Writing to a File (Asynchronous):** ```javascript const fs = require('fs'); fs.writeFile('output.txt', 'Hello, Node.js!', (err) => { if (err) throw err; console.log('File written successfully.'); }); ``` * **Appending to a File (Asynchronous):** ```javascript const fs = require('fs'); fs.appendFile('output.txt', '\nAppended text.', (err) => { if (err) throw err; console.log('Text appended successfully.'); }); ``` #### **Handling Paths with** `path` Module * **path module:** * Helps with working with file and directory paths. It's especially useful when you need to manipulate or join paths across platforms. * **Joining Paths:** ```javascript const path = require('path'); const fullPath = path.join(__dirname, 'files', 'example.txt'); console.log('Full Path:', fullPath); ``` * **Getting File Name from Path:** ```javascript const path = require('path'); const filePath = '/users/documents/example.txt'; console.log('File Name:', path.basename(filePath)); ``` * **Getting Directory Name from Path:** ```javascript const path = require('path'); const filePath = '/users/documents/example.txt'; console.log('Directory Name:', path.dirname(filePath)); ``` --- #### **Timing Events with** `setTimeout` and `setInterval` * `setTimeout`: Runs a function after a certain delay (once). ```javascript setTimeout(() => { console.log('This runs after 3 seconds'); }, 3000); // 3000 milliseconds = 3 seconds ``` * `setInterval`: Runs a function repeatedly after a specified interval. ```javascript setInterval(() => { console.log('This runs every 2 seconds'); }, 2000); // 2000 milliseconds = 2 seconds ``` * **Clearing Intervals:** ```javascript const intervalId = setInterval(() => { console.log('Repeating...'); }, 1000); setTimeout(() => { clearInterval(intervalId); console.log('Stopped interval'); }, 5000); // Stop after 5 seconds ``` * ### **Working with Modules and npm** * [![](https://cdn.hashnode.com/res/hashnode/image/upload/v1727111022929/0132c432-6878-4972-a628-adeab241dab5.png align="center")](https://spectrumstutz.wordpress.com/wp-content/uploads/2022/10/03275-nodejs-npm-01-1.png) #### **1\. Theory:** --- #### **Modular Programming in Node.js** * **What is Modular Programming?** * **Modular programming** is about breaking a program into smaller, reusable parts (called modules). Each module contains related functionality, making code easier to maintain and scale. * **Node.js uses CommonJS module system**, which includes: * `require()`: Used to load modules. * `module.exports`: Used to export functionality from a module so other files can use it. --- #### **CommonJS: How Modules Work in Node.js** * **Creating a module:** * In Node.js, you can create your own module by writing code in a separate file and exporting the functionality you want to reuse. * **Using** `require()` to load a module: * To use a module in another file, you load it with `require()`. **Example:** ```javascript // math.js (your custom module) function add(a, b) { return a + b; } function subtract(a, b) { return a - b; } // Exporting the functions module.exports = { add, subtract }; ``` * Now, you can use the `add` and `subtract` functions from `math.js` in another file: ```javascript // main.js const math = require('./math'); console.log(math.add(5, 3)); // Output: 8 console.log(math.subtract(10, 7)); // Output: 3 ``` --- #### **What is npm and Package Management?** * **What is npm?** * npm (Node Package Manager) is the default package manager for Node.js. It helps install, manage, and share reusable packages of code. * npm allows you to easily download and integrate thousands of third-party libraries (packages) like `lodash`, `axios`, etc., into your project. * **Package Management:** * Packages are collections of code that can be easily installed and managed using npm. They are stored in a registry (like npm's registry) and can be added to your project with simple commands. --- #### **Introduction to** `package.json` and Dependencies * **What is** `package.json`? * `package.json` is a file that holds metadata about your Node.js project (like project name, version, and dependencies). It is automatically generated when you run the `npm init` command. * **Dependencies:** * Dependencies are packages your project relies on. They are listed in `package.json` so they can be easily installed on any machine using `npm install`. --- ### **3\. Tasks for Day 2:** 1. **Task 1: File Operations** * **What to do:** * Create a new file called `notes.txt` and write "Learning Node.js" into it. * Read and display the content of `notes.txt`. * Append "Node.js is awesome!" to the same file and read it again. 2. **Task 2: Path Operations** * **What to do:** * Use the `path` module to print the full path of your `notes.txt` file. * Extract and print only the file name from the path. * Extract and print the directory name from the path. 3. **Task 3: Timing Events** * **What to do:** * Write a `setTimeout` function to print "Hello after 3 seconds." * Use `setInterval` to print "Learning is fun!" every 2 seconds and stop it after 10 seconds using `clearInterval`. 4. **Reflection:** * Write a paragraph about your understanding of synchronous and asynchronous programming. Explain the difference in your own words. --- ### **Additional Resources:** * Node.js Official Documentation * Understanding the Node.js Event Loop --- ### **Summary:** * **Theory**: Focus on core modules like `fs`, `path`, and the Node.js event loop. * **Practical**: Perform file operations, handle paths, and understand timing events with `setTimeout` and `setInterval`. * **Tasks**: Reinforce learning by writing and manipulating files, handling paths, and experimenting with asynchronous timers.