🎯 What You’ll Learn Today:

• What is the fs module?

• How to read and write files

• Synchronous vs Asynchronous methods

• Real-life examples

• Best practices for working professionals

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📦 What is the fs Module?

The fs module (short for File System) is a core module in Node.js.
It helps us create, read, update, and delete files and folders in your computer system — using JavaScript.

You don’t need to install it. It's built into Node.js. Just use:

const fs = require('fs');

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🔍 Why is the fs Module Useful?

📌 Imagine you are:

• Creating a blog and want to save blog posts as files.

• Making a log system to store user activity.

• Reading a config or setting file.

• Creating user reports in text format.

These things can easily be done using the fs module.

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✍️ 1. Writing to a File (Create or Overwrite)

➤ Synchronous Way

const fs = require('fs');

fs.writeFileSync('data.txt', 'Hello, this is written by Node.js!');
console.log('File written successfully!');

✅ This creates a new file data.txt or overwrites if already exists.

---

➤ Asynchronous Way (Recommended)

const fs = require('fs');

fs.writeFile('info.txt', 'This is async writing!', (err) => {
  if (err) {
    console.log('Error writing file:', err);
  } else {
    console.log('File written successfully (async)!');
  }
});

💡 Async is better in real-world apps because it doesn’t block other operations.

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📖 2. Reading a File

➤ Synchronous Way

const data = fs.readFileSync('data.txt', 'utf-8');
console.log('File Content:', data);

---

➤ Asynchronous Way

fs.readFile('info.txt', 'utf-8', (err, data) => {
  if (err) {
    console.log('Error reading file:', err);
  } else {
    console.log('File Content:', data);
  }
});

💡 Always use 'utf-8' to read the content as text. Without it, you'll get a buffer.

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➕ 3. Appending to a File

fs.appendFileSync('data.txt', '\nThis is a new line added!');

This will add a new line to the existing content of data.txt.

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❌ 4. Deleting a File

fs.unlinkSync('info.txt');
console.log('File deleted!');

Be careful while using this. It permanently deletes the file.

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📂 5. Creating a Folder (Directory)

fs.mkdirSync('myFolder');
console.log('Folder created!');

You can now write files into this folder.

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🧠 Real-Life Example: Saving User Feedback in a File

Suppose you’re building a backend app for collecting feedback. You want to store feedback in a file.

➤ feedback.js

const fs = require('fs');

const name = "Rahul";
const message = "This course is amazing!";
const feedback = `Name: ${name}\nFeedback: ${message}\n-----------------\n`;

fs.appendFile('feedback.txt', feedback, (err) => {
  if (err) {
    console.log("Couldn't save feedback");
  } else {
    console.log("Feedback saved successfully!");
  }
});

✅ Every time you run this file, a new feedback will be added to feedback.txt.

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🧰 Best Practices for Working Professionals

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💼 Bonus: Using fs.promises with async/await

const fs = require('fs/promises');

async function readMyFile() {
  try {
    const content = await fs.readFile('data.txt', 'utf-8');
    console.log('File:', content);
  } catch (err) {
    console.log('Error:', err);
  }
}

readMyFile();

📌 This is the modern way professionals use fs in real projects.

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📝 Practice Tasks for You

1. Create a file bio.txt and write your name, age, and goal.

2. Append one new line every time you run the file.

3. Try reading the file and showing output on the console.

4. Create a folder logs, and write logs inside logs/log.txt.

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✅ Summary

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🎉 You now know how to manage files and folders using Node.js like a backend pro!

❓ Frequently Asked Questions (FAQs)

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1) We use writeFile() instead of writeFileSync() in real projects. Can we use .appendFile() instead of .appendFileSync() too?

✅ Yes, absolutely!
Just like writeFileSync() has an asynchronous version writeFile(),
appendFileSync() also has an async version called appendFile().

Here’s how you use it:

const fs = require('fs');

fs.appendFile('data.txt', '\nThis is a new async line!', (err) => {
  if (err) throw err;
  console.log('Line appended asynchronously!');
});

🔁 So, always prefer async methods (appendFile, writeFile, etc.) in real-world applications to avoid blocking your server.

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2) Can we use an async version of unlinkSync()?

✅ Yes!
The async version is simply: fs.unlink()

Example:

fs.unlink('data.txt', (err) => {
  if (err) throw err;
  console.log('File deleted asynchronously!');
});

So, in professional apps, prefer:

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3) Is there an async version of mkdirSync()?

✅ Yes!
Use fs.mkdir() instead of fs.mkdirSync() for asynchronous folder creation.

fs.mkdir('logs', (err) => {
  if (err) throw err;
  console.log('Folder created asynchronously!');
});

📌 If the folder already exists, it may throw an error. You can pass { recursive: true } to create nested folders safely:

fs.mkdir('logs/subfolder', { recursive: true }, (err) => {
  if (err) throw err;
  console.log('Nested folder created!');
});

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🧠 Quick Comparison Table

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✅ Recommendation:
Use async versions in all real projects to keep your server fast and non-blocking.

Sync methods can be used for:

• Quick scripts

• Learning/demo projects

• CLI utilities where performance isn’t critical

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