Node.js Core Modules Review

## Introduction to Node.js Core Modules - **Node.js Core Modules**: Built-in modules that come pre-installed with Node.js, providing essential functionality for file operations, cryptography, operating system interactions, and more. - **Standard Modules**: No need for separate installation; available as long as Node.js is installed. - **Import Syntax**: Use `require()` to import core modules into your application. ```javascript const fs = require("fs"); const crypto = require("crypto"); const os = require("os"); ``` ## File System (fs) Module - **Purpose**: Provides methods for working with files and folders, including opening, closing, reading, writing, and deleting operations. - **Import**: `const fs = require("fs");` - **Flexibility**: Methods available in three forms: callbacks, promises, and synchronous. ### Method Usage Patterns - **Asynchronous with Callbacks**: Default behavior, non-blocking. ```javascript fs.writeFile("filePath", "content", "utf8", (err) => { if (err) throw err; console.log("File written to!"); }); ``` - **Promises-based**: Preferred for modern applications, uses `async/await`. ```javascript const fs = require("fs/promises"); async function writeToFile() { try { await fs.writeFile("article.md", "## Node fs Module"); console.log("File written to!"); } catch (err) { console.error(err); } } ``` - **Synchronous**: Blocking operation, suitable for simple scripts. ```javascript try { fs.writeFileSync("article.md", "## Node fs Module", "utf8"); console.log("File written to!"); } catch (err) { console.error(err); } ``` ### Core File Operations - **`writeFile()` Method**: Creates or overwrites a file with specified content. ```javascript await fs.writeFile("article.md", "## Node fs Module: The Complete Guide"); ``` - **`appendFile()` Method**: Adds content to the end of an existing file. ```javascript await fs.appendFile("article.md", "\n\nIn this article, you will learn..."); ``` - **`readFile()` Method**: Reads the contents of a file. ```javascript const content = await fs.readFile("article.md", "utf8"); console.log("File content:", content); ``` - **`unlink()` Method**: Deletes a file from the file system. ```javascript await fs.unlink("article.md"); console.log("File deleted successfully"); ``` ### Character Encoding - **UTF-8 Encoding**: Specify `"utf8"` to read files as text strings. - **Buffer Format**: Without encoding specification, files are read as binary buffer objects. ```javascript // Returns string const textContent = await fs.readFile("file.txt", "utf8"); // Returns Buffer const bufferContent = await fs.readFile("file.txt"); ``` ## Buffer Module - **Purpose**: Handles binary data directly in memory for files, images, and network streams. - **Import**: `const { Buffer } = require("buffer");` - **Use Cases**: File I/O, TCP streams, image processing, and binary data manipulation. ### Buffer Creation - **`Buffer.from()` Method**: Creates buffer from strings, arrays, or other data. ```javascript // From string const myStrBuffer = Buffer.from("freeCodeCamp"); console.log(myStrBuffer); // <Buffer 66 72 65 65 43 6f 64 65 43 61 6d 70> // From array of numbers const myNumBuffer = Buffer.from([70, 82, 69, 69, 67, 79, 68, 69, 67, 65, 77, 80]); ``` - **`Buffer.alloc()` Method**: Creates buffer of specified size filled with zeros. ```javascript const someBuffer = Buffer.alloc(10); console.log(someBuffer); // <Buffer 00 00 00 00 00 00 00 00 00 00> ``` ### Buffer Operations - **Array-like Access**: Access individual buffer elements using index notation. ```javascript console.log(myStrBuffer[0]); // 102 (byte value for 'f') ``` - **`toString()` Method**: Converts buffer to readable string. ```javascript console.log(myStrBuffer.toString()); // "freeCodeCamp" ``` - **`Buffer.write()` Method**: Writes data to an allocated buffer. ```javascript someBuffer.write("Hello fCC"); console.log(someBuffer.toString()); // "Hello fCC" ``` - **`Buffer.byteLength()` Method**: Returns number of bytes needed to store a string. ```javascript console.log(Buffer.byteLength("Hello freeCodeCamp")); // 18 ``` ### Additional Buffer Methods - **`Buffer.isBuffer()`**: Checks if an object is a buffer. - **`Buffer.compare()`**: Compares two buffers and returns sort order. - **`Buffer.concat()`**: Joins multiple buffers into one. ## Crypto Module - **Purpose**: Provides cryptographic functionality, including hashing, encryption, decryption, and digital signatures. - **Import**: `const crypto = require("crypto");` - **Security Note**: Use well-tested libraries like `bcrypt` or `jsonwebtoken` for production authentication. ### Hashing Methods - **`createHash()` Method**: Creates one-way hash using algorithms like SHA256, SHA512, or MD5. ```javascript const hashedPassword = crypto .createHash("sha256") .update("myPassword123") .digest("hex"); console.log("createHash result:", hashedPassword); ``` - **`createHmac()` Method**: Creates a hash with a secret key for authentication and data integrity. ```javascript const hashedMessage = crypto .createHmac("sha256", "secret-key") .update("Hello World") .digest("hex"); ``` ### Encryption and Decryption - **`createCipheriv()` and `createDecipheriv()` Methods**: Encrypt and decrypt data using algorithms, keys, and initialization vectors. ```javascript const key = Buffer.from("12345678901234567890123456789012"); // 32 bytes for AES-256 const iv = Buffer.from("1234567890123456"); // 16 bytes for AES // Encryption const cipher = crypto.createCipheriv("aes-256-cbc", key, iv); let encrypted = cipher.update("Hello campers!", "utf8", "hex"); encrypted += cipher.final("hex"); // Decryption const decipher = crypto.createDecipheriv("aes-256-cbc", key, iv); let decrypted = decipher.update(encrypted, "hex", "utf8"); decrypted += decipher.final("utf8"); ``` ### Random Value Generation - **`randomBytes()` Method**: Generates cryptographically secure random bytes. ```javascript console.log("Random Bytes:", crypto.randomBytes(16).toString("hex")); // Output: a6154ef5a296fa176ad0f332bd94d712 ``` - **`randomInt()` Method**: Generates secure random integers within specified range. ```javascript console.log("Random Int:", crypto.randomInt(0, 100)); // Random number 0-99 ``` ### Key Management - **`createSecretKey()` Method**: Creates cryptographic key objects from raw bytes. ```javascript const secret = crypto.createSecretKey(crypto.randomBytes(32)); console.log(secret.export().toString('hex')); ``` ### Digital Signatures - **`sign()` and `verify()` Methods**: Create and validate digital signatures using private/public key pairs. - **Use Case**: Proves data authenticity and integrity. ### Additional Crypto Methods - **`createPublicKey()` and `createPrivateKey()`**: Work with externally generated keys. - **`createDiffieHellman()`**: Enables secure shared secret generation. - **`Certificate()`**: Handles HTTPS certificate operations. ## OS Module - **Purpose**: Provides operating system-related utilities for system information and cross-platform compatibility. - **Import**: `const os = require("os");` - **Use Cases**: System monitoring, cross-platform scripting, hardware information. ### System Information Methods - **`platform()` Method**: Returns operating system platform. ```javascript console.log(os.platform()); // 'darwin', 'win32', 'linux', etc. // Cross-platform usage if (os.platform() === 'win32') { // Windows-specific code } else { // Unix-like systems } ``` - **`arch()` Method**: Returns CPU architecture. ```javascript console.log(os.arch()); // 'arm64', 'x64', 'arm', 'ia32', etc. ``` - **`type()` Method**: Returns official operating system name. ```javascript console.log(os.type()); // 'Darwin', 'Linux', 'Windows_NT' ``` ### Version Information - **`release()` Method**: Shows OS kernel version. ```javascript console.log(os.release()); // '25.0.0' ``` - **`version()` Method**: Returns detailed OS version information. ```javascript console.log(os.version()); // Darwin Kernel Version 25.0.0: Wed Sep 17 21:41:39 PDT 2025 ``` ### Hardware Information - **`cpus()` Method**: Returns an array of CPU core information. ```javascript console.log(os.cpus()); // Array of CPU core objects with model, speed, times ``` - **`uptime()` Method**: Returns system uptime in seconds. ```javascript console.log(os.uptime()); // 23047 (seconds since system boot) ``` ### Memory Information - **`totalmem()` Method**: Returns total system memory in bytes. - **`freemem()` Method**: Returns available system memory in bytes. ## Best Practices ### Performance Considerations - **Avoid Synchronous Methods**: Use asynchronous methods in production applications to prevent blocking. - **Prefer Promises**: Use `async/await` with promises-based API for cleaner, maintainable code. - **Error Handling**: Always implement proper error handling with try-catch blocks or error callbacks. ### Security Guidelines - **Crypto Module**: Use established libraries for authentication rather than building custom crypto solutions. - **Input Validation**: Validate file paths and user input to prevent security vulnerabilities. - **Key Management**: Store cryptographic keys securely, never hardcode them in source code. ### Cross-Platform Development - **OS Module Usage**: Use OS module methods for cross-platform compatibility. - **Path Handling**: Use `path` module for cross-platform file path operations. - **Environment Variables**: Check platform-specific environment variables and configurations. ## Common Use Cases ### File Operations - Configuration file management - Log file creation and maintenance - Data export/import functionality - Template processing ### Data Security - Password hashing for user authentication - Data encryption for sensitive information - Random token generation for sessions - Digital signature verification ### System Integration - Cross-platform application deployment - System resource monitoring - Hardware compatibility checks - Performance optimization based on system capabilities