File System (fs) Module
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Author & Reviewer
Learn how to use the built-in fs (File System) module to read, write, and manage files directly on your computer's hard drive.
Learning Goals
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The Core Concept
One of the superpowers Node.js gives JavaScript is the ability to interact with your computer's files. The `fs` (File System) module allows your code to create folders, read text files, and save data.
The most important rule when dealing with files is to always use **asynchronous** methods. Reading a large file takes time. If you use synchronous (blocking) methods, your entire Node.js server will freeze and ignore all other users until the file finishes loading. In modern Node.js, we use the `fs/promises` version of the module so we can use `async/await` syntax, making the code clean and readable.
### Best Practices
- Always use `fs/promises` instead of the older callback-based `fs` module.
- Use `try/catch` blocks. If you try to read a file that doesn't exist, your app will crash unless you catch the error.
### Common Mistakes
- Using `fs.readFileSync()` in a web server route. This blocks all other incoming requests.
### Interview Questions 1. **What happens if you use fs.readFileSync in a busy web server?** *Answer:* It blocks the Event Loop, causing the server to freeze for all users until the file is read.
Visual guide
Node.js concept flow
A simple original diagram to connect the lesson idea with real project flow.
Code & Implementation
// We import the promises version of the fs module
const fs = require('fs/promises');
async function manageFiles() {
try {
// 1. Write text to a new file
await fs.writeFile('message.txt', 'Hello, this file was created by Node.js!');
console.log('File successfully created.');
// 2. Read the file back
const data = await fs.readFile('message.txt', 'utf8');
console.log('File content:', data);
} catch (error) {
// 3. Catch errors (like permission denied)
console.error('An error occurred:', error.message);
}
}
manageFiles();Expected Output
File successfully created. File content: Hello, this file was created by Node.js!
Automated Log Creator
Hands-on practice task
The Challenge
Write an async function that creates a file named 'app.log' and writes the current date and time into it.
Helpful Hints
- •Use new Date().toString() to get the current time.
- •Use await fs.writeFile('app.log', text).
Quick Knowledge Check
Why did I get <Buffer 48 65 6c...> instead of text when reading a file?
Continue Learning
Next steps after this lesson
Write an async function that creates a file named 'app.log' and writes the current date and time into it.
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