File System

Reading Files

Node.js provides the fs module for file system operations. The modern fs/promises API is the recommended approach.

import { readFile, readdir, stat } from 'fs/promises';
import { createReadStream } from 'fs';
import path from 'path';

// Read entire file
async function readConfig(filename: string): Promise<object> {
  const filepath = path.join(process.cwd(), 'config', filename);
  const content = await readFile(filepath, 'utf-8');
  return JSON.parse(content);
}

// List directory contents
async function listFiles(dir: string): Promise<string[]> {
  const entries = await readdir(dir, { withFileTypes: true });
  return entries
    .filter(entry => entry.isFile())
    .map(entry => entry.name);
}

// Get file info
async function getFileInfo(filepath: string) {
  const stats = await stat(filepath);
  return {
    size: stats.size,
    created: stats.birthtime,
    modified: stats.mtime,
    isFile: stats.isFile(),
    isDirectory: stats.isDirectory(),
  };
}

// Stream large files (memory efficient)
function streamFile(filepath: string): Promise<string> {
  return new Promise((resolve, reject) => {
    const chunks: Buffer[] = [];
    const stream = createReadStream(filepath);

    stream.on('data', chunk => chunks.push(Buffer.from(chunk)));
    stream.on('end', () => resolve(Buffer.concat(chunks).toString()));
    stream.on('error', reject);
  });
}

Writing & Managing Files

Writing files, creating directories, and managing file system paths are common Node.js tasks.

import { writeFile, appendFile, mkdir, rm, copyFile, rename } from 'fs/promises';
import { existsSync } from 'fs';
import path from 'path';

// Write a file (creates or overwrites)
async function saveConfig(data: object, filename: string): Promise<void> {
  const content = JSON.stringify(data, null, 2);
  await writeFile(filename, content, 'utf-8');
  console.log(`Saved ${filename}`);
}

// Append to a log file
async function log(message: string): Promise<void> {
  const timestamp = new Date().toISOString();
  const entry = `[${timestamp}] ${message}\n`;
  await appendFile('app.log', entry, 'utf-8');
}

// Create nested directories
async function ensureDir(dirPath: string): Promise<void> {
  await mkdir(dirPath, { recursive: true }); // Creates parent dirs too
}

// Safe file operations with error handling
async function safeWriteFile(filepath: string, content: string): Promise<boolean> {
  try {
    const dir = path.dirname(filepath);
    await mkdir(dir, { recursive: true });
    await writeFile(filepath, content, 'utf-8');
    return true;
  } catch (error) {
    console.error(`Failed to write ${filepath}:`, error);
    return false;
  }
}

// Move/rename files
async function moveFile(src: string, dest: string): Promise<void> {
  await ensureDir(path.dirname(dest));
  await rename(src, dest);
}