The Node.js fs (File System) module provides APIs for interacting with the local file system using Promises, callbacks, or synchronous execution.
Promise-Based API (Modern ESM / CJS)
const fs = require('fs/promises');
// import fs from 'node:fs/promises';
// Read file as UTF-8 string
const content = await fs.readFile('data.txt', 'utf8');
// Write or replace file contents
await fs.writeFile('output.txt', 'Hello World', 'utf8');
// Append to file
await fs.appendFile('log.txt', 'New entry\n', 'utf8');
// Check existence & access permissions
try {
await fs.access('config.json');
} catch {
console.log('File does not exist or cannot be accessed');
}
Synchronous API
const fs = require('fs');
const data = fs.readFileSync('input.txt', 'utf8');
fs.writeFileSync('output.txt', data);
fs.appendFileSync('output.txt', '\nappended');
const exists = fs.existsSync('file.txt');
File Metadata & Stats
const stats = await fs.stat('file.txt');
stats.isFile(); // -> true / false
stats.isDirectory(); // -> true / false
stats.isSymbolicLink(); // -> true / false
stats.size; // File size in bytes
stats.mtime; // Last modified timestamp
Directory Operations
// List directory entries
const files = await fs.readdir('src/');
// Recursive directory creation
await fs.mkdir('build/assets/css', { recursive: true });
// Recursive directory removal
await fs.rm('dist/', { recursive: true, force: true });
File System Watching
const fs = require('fs');
const watcher = fs.watch('src/', { recursive: true }, (eventType, filename) => {
console.log(`Event: ${eventType} on ${filename}`);
});
// Stop watching
watcher.close();