File System Module in Node.js

The File System (fs) module allows Node.js to interact with files and directories on the system.
It is a core module, so no installation is required.

const fs = require('fs');

1. Types of File System Operations

The fs module supports three styles of operations:

1.1 Synchronous (Blocking)

• Executes operations sequentially

• Blocks the event loop

• Suitable for scripts and startup tasks

Example:

const data = fs.readFileSync('file.txt', 'utf8');
console.log(data);

1.2 Asynchronous (Callback-based)

• Non-blocking

• Uses callbacks

• Preferred for production apps

Example:

fs.readFile('file.txt', 'utf8', (err, data) => {
  if (err) throw err;
  console.log(data);
});

1.3 Promise-based (fs/promises)

• Uses Promises and async/await

• Clean and modern approach

Example:

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

const data = await fs.readFile('file.txt', 'utf8');

2. Common File Operations

2.1 Reading Files

fs.readFile('a.txt', 'utf8', callback);
fs.readFileSync('a.txt', 'utf8');

2.2 Writing Files

fs.writeFile('a.txt', 'Hello', callback);
fs.writeFileSync('a.txt', 'Hello');

2.3 Appending Files

fs.appendFile('a.txt', '\nNew line', callback);

2.4 Deleting Files

fs.unlink('a.txt', callback);

3. Directory Operations

3.1 Create Directory

fs.mkdir('myFolder', callback);

3.2 Read Directory

fs.readdir('myFolder', callback);

3.3 Remove Directory

fs.rmdir('myFolder', callback);

4. File Information (Stats)

fs.stat('file.txt', (err, stats) => {
  console.log(stats.isFile());
  console.log(stats.size);
});

5. File Streams

Streams allow reading/writing large files efficiently.

5.1 Read Stream

const readStream = fs.createReadStream('big.txt');
readStream.on('data', chunk => {
  console.log(chunk.toString());
});

5.2 Write Stream

const writeStream = fs.createWriteStream('out.txt');
writeStream.write('Hello Stream');

6. File Permissions

fs.chmod('file.txt', 0o644, callback);

7. Watching Files

fs.watch('file.txt', (eventType, filename) => {
  console.log(eventType);
});

8. Error Handling

Always handle errors properly:

if (err) {
  console.error(err);
  return;
}

9. When to Use Which Method

10. Advantages of fs Module

• Built-in and fast

• Supports sync & async

• Handles files and directories

• Stream support for large data

11. Summary

• fs is a core Node.js module

• Supports synchronous, asynchronous, and promise-based APIs

• Used for file and directory operations

• Streams improve performance for large files