File System Basics

Imagine you have a diary where you write notes, read them later, and sometimes tear out pages. In Node.js, the **File System (fs) module** lets you do exactly that with files on your computer – create, read, update, and delete files.

What is the File System Module?

The fs module provides an API for interacting with the file system in a way modeled on standard POSIX functions. It lets you work with files and directories – reading, writing, deleting, renaming, and more.

Think of the fs module as your personal file manager – but instead of clicking and dragging, you write code to do it.

Two Ways to Use fs Module

The fs module provides both synchronous and asynchronous methods:

Synchronous: Blocking – waits for operation to complete. Method names end with `Sync`.
Asynchronous: Non-blocking – takes a callback. This is the preferred way in Node.js.

Importing the fs Module

const fs = require('fs');

Reading Files (Asynchronous)

<!-- Create a file called sample.txt with some content -->

fs.readFile('sample.txt', 'utf8', (err, data) => {
  if (err) {
    console.error('Error reading file:', err);
    return;
  }
  console.log('File content:', data);
});

console.log('Reading file... (this prints first!)');

Reading Files (Synchronous)

try {
  const data = fs.readFileSync('sample.txt', 'utf8');
  console.log('File content:', data);
} catch (err) {
  console.error('Error reading file:', err);
}
console.log('This prints after reading (synchronous)');

Writing Files

<!-- Asynchronous write -->
const content = 'Hello, this is a new file!nCreated with Node.js';

fs.writeFile('newfile.txt', content, 'utf8', (err) => {
  if (err) {
    console.error('Error writing file:', err);
    return;
  }
  console.log('File written successfully!');
});

<!-- Synchronous write -->
try {
  fs.writeFileSync('sync-file.txt', 'Synchronous write');
  console.log('Sync file written');
} catch (err) {
  console.error(err);
}

Appending to Files

Add content to the end of an existing file.

fs.appendFile('newfile.txt', 'nThis line is appended.', (err) => {
  if (err) throw err;
  console.log('Content appended!');
});

Checking if a File Exists

<!-- Modern way (since Node.js v10) -->
const fsPromises = require('fs').promises;

async function checkFile() {
  try {
    await fsPromises.access('sample.txt');
    console.log('File exists');
  } catch {
    console.log('File does not exist');
  }
}

checkFile();

Deleting Files

fs.unlink('file-to-delete.txt', (err) => {
  if (err) {
    console.error('Error deleting file:', err);
    return;
  }
  console.log('File deleted successfully');
});

Error Handling is Important!

Always handle errors when working with files – files might not exist, permissions might be wrong, disks might be full.

<!-- Asynchronous with proper error handling -->
fs.readFile('nonexistent.txt', 'utf8', (err, data) => {
  if (err) {
    if (err.code === 'ENOENT') {
      console.log('File not found!');
    } else {
      console.error('Other error:', err);
    }
    return;
  }
  console.log(data);
});

Working with File Descriptors (Advanced)

For more control, you can open files and work with file descriptors:

fs.open('data.txt', 'r', (err, fd) => {
  if (err) throw err;
  
  <!-- Read from the file using the file descriptor -->
  const buffer = Buffer.alloc(100);
  fs.read(fd, buffer, 0, buffer.length, 0, (err, bytesRead, buffer) => {
    console.log(buffer.toString('utf8', 0, bytesRead));
    
    <!-- Always close the file descriptor -->
    fs.close(fd, (err) => {
      if (err) throw err;
    });
  });
});

Two Minute Drill

fs module lets you work with files – read, write, append, delete.
Use asynchronous methods (callbacks) for non-blocking operations.
Synchronous methods (with `Sync`) are simpler but block the event loop.
Always handle errors – files may not exist or permissions may be wrong.
For modern code, consider using `fs.promises` with async/await.

Need more clarification?

Drop us an email at career@quipoinfotech.com

Welcome to Quipoin

Quipoin Menu

File System Basics

Need more clarification?