File System Operations

The fs Module

The fs (file system) module provides an API for interacting with the file system. It offers both synchronous and asynchronous methods, as well as a promises-based API.

Reading Files

const fs = require('fs');
const path = require('path');

// Asynchronous (callback-based)
fs.readFile('example.txt', 'utf8', (err, data) => {
  if (err) {
    console.error('Error reading file:', err);
    return;
  }
  console.log(data);
});

// Synchronous (blocks execution)
try {
  const data = fs.readFileSync('example.txt', 'utf8');
  console.log(data);
} catch (err) {
  console.error('Error:', err);
}

// Promise-based (recommended)
const fsPromises = require('fs').promises;

async function readFile() {
  try {
    const data = await fsPromises.readFile('example.txt', 'utf8');
    console.log(data);
  } catch (err) {
    console.error('Error:', err);
  }
}

readFile();

Writing Files

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

// Write a new file (overwrites if exists)
async function writeFile() {
  await fs.writeFile('output.txt', 'Hello, Node.js!');
  console.log('File written successfully');
}

// Append to a file
async function appendToFile() {
  await fs.appendFile('log.txt', 'New log entry\n');
  console.log('Content appended');
}

// Write JSON data
async function writeJSON() {
  const data = {
    name: 'John',
    age: 30,
    skills: ['JavaScript', 'Node.js']
  };
  
  await fs.writeFile(
    'data.json', 
    JSON.stringify(data, null, 2)  // Pretty print with 2 spaces
  );
}

writeJSON();

Working with Directories

const fs = require('fs').promises;
const path = require('path');

// Create a directory
async function createDir() {
  await fs.mkdir('new-folder', { recursive: true });
  // recursive: true creates parent directories if needed
}

// Read directory contents
async function listFiles() {
  const files = await fs.readdir('.');
  console.log('Files:', files);
  
  // With file type information
  const entries = await fs.readdir('.', { withFileTypes: true });
  entries.forEach(entry => {
    const type = entry.isDirectory() ? 'DIR' : 'FILE';
    console.log(`[${type}] ${entry.name}`);
  });
}

// Remove a directory
async function removeDir() {
  await fs.rmdir('old-folder', { recursive: true });
}

// Check if file/directory exists
async function checkExists(filePath) {
  try {
    await fs.access(filePath);
    return true;
  } catch {
    return false;
  }
}

File Information & Stats

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

async function getFileInfo(filePath) {
  const stats = await fs.stat(filePath);
  
  console.log('Is file:', stats.isFile());
  console.log('Is directory:', stats.isDirectory());
  console.log('File size:', stats.size, 'bytes');
  console.log('Created:', stats.birthtime);
  console.log('Modified:', stats.mtime);
}

getFileInfo('package.json');

Copying, Moving & Deleting

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

// Copy a file
async function copyFile() {
  await fs.copyFile('source.txt', 'destination.txt');
}

// Rename/Move a file
async function moveFile() {
  await fs.rename('old-name.txt', 'new-name.txt');
  // Also works for moving to different directory
  await fs.rename('file.txt', 'subfolder/file.txt');
}

// Delete a file
async function deleteFile() {
  await fs.unlink('unwanted-file.txt');
}

The path Module

Use the path module for cross-platform path handling:

const path = require('path');

// Join path segments
const fullPath = path.join(__dirname, 'data', 'file.txt');
// /Users/you/project/data/file.txt

// Get file extension
console.log(path.extname('image.png'));  // .png

// Get filename
console.log(path.basename('/path/to/file.txt'));       // file.txt
console.log(path.basename('/path/to/file.txt', '.txt')); // file

// Get directory name
console.log(path.dirname('/path/to/file.txt'));  // /path/to

// Parse path into components
const parsed = path.parse('/home/user/file.txt');
console.log(parsed);
// { root: '/', dir: '/home/user', base: 'file.txt', ext: '.txt', name: 'file' }

// Resolve to absolute path
console.log(path.resolve('data', 'file.txt'));
// /Users/you/project/data/file.txt

Practical Example: File Processor

const fs = require('fs').promises;
const path = require('path');

async function processFiles(directory) {
  const entries = await fs.readdir(directory, { withFileTypes: true });
  
  for (const entry of entries) {
    const fullPath = path.join(directory, entry.name);
    
    if (entry.isDirectory()) {
      // Recursively process subdirectories
      await processFiles(fullPath);
    } else if (entry.name.endsWith('.txt')) {
      // Process text files
      const content = await fs.readFile(fullPath, 'utf8');
      const wordCount = content.split(/\s+/).length;
      console.log(`${entry.name}: ${wordCount} words`);
    }
  }
}

processFiles('./documents');