Node.js Configuration

/**
 * Node.js ESLint configuration
 * Accessible as: "node" or "recommended/node"
 */
env:
  node: true              # Enable Node.js global variables and scoping

extends: esnext           # Inherit all ESNext rules and configuration

rules:
  no-path-concat: 2                  # Error: disallow string concatenation with __dirname/__filename
  no-process-exit: 2                 # Error: disallow the use of process.exit()
  no-sync: 1                         # Warning: disallow synchronous methods
  import/no-nodejs-modules: 0        # Disabled: allow importing Node.js built-in modules

/**
 * Node.js-specific linting rules
 */
rules: {
  /**
   * no-path-concat: Disallow string concatenation with __dirname and __filename
   * Level: Error (2)
   * Prevents unsafe path construction that may fail on different operating systems
   */
  "no-path-concat": "error",
  
  /**
   * no-process-exit: Disallow the use of process.exit()
   * Level: Error (2)  
   * Prevents abrupt process termination that bypasses cleanup and error handling
   */
  "no-process-exit": "error",
  
  /**
   * no-sync: Disallow synchronous methods
   * Level: Warning (1)
   * Warns against blocking the event loop with synchronous operations
   */
  "no-sync": "warn",
  
  /**
   * import/no-nodejs-modules: Allow importing Node.js built-in modules
   * Level: Disabled (0) - overrides ESNext configuration
   * Permits importing Node.js core modules like 'fs', 'path', 'http', etc.
   */
  "import/no-nodejs-modules": "off"
}

# .eslintrc.yaml
extends:
  - node

# Optional project-specific rules
rules:
  no-console: warn

# .eslintrc.yaml
extends:
  - node

rules:
  # Stricter for production servers
  no-console: error
  no-sync: error
  
  # Allow process.exit in CLI scripts
  no-process-exit: off

env:
  # Add additional environments
  jest: true

overrides:
  # Allow console in development/test files
  - files: ['**/*.test.js', '**/*.spec.js', 'scripts/**/*.js']
    rules:
      no-console: off

# .eslintrc.yaml
extends:
  - node

rules:
  # Common Express patterns
  no-unused-vars: [error, { argsIgnorePattern: '^(req|res|next)$' }]
  
  # Allow callback pattern
  consistent-return: off

# .eslintrc.yaml
extends:
  - node

rules:
  # CLI tools often need these
  no-console: off
  no-process-exit: off
  no-sync: off

// ❌ Error: String concatenation with __dirname
const configPath = __dirname + '/config.json';
const logPath = __dirname + '/../logs/app.log';
const templatePath = __filename + '.template';

// ✅ Correct: Use path.join()
const path = require('path');
const configPath = path.join(__dirname, 'config.json');
const logPath = path.join(__dirname, '..', 'logs', 'app.log');
const templatePath = path.join(path.dirname(__filename), path.basename(__filename) + '.template');

// ✅ Also correct: Use path.resolve() for absolute paths
const configPath = path.resolve(__dirname, 'config.json');

// ❌ Error: Direct process.exit() call
if (error) {
  console.error('Fatal error:', error);
  process.exit(1);
}

if (!config.apiKey) {
  console.error('API key required');
  process.exit(1);
}

// ✅ Correct: Throw error for proper error handling
if (error) {
  throw new Error(`Fatal error: ${error.message}`);
}

if (!config.apiKey) {
  throw new Error('API key required');
}

// ✅ Also correct: Set exit code and let process end naturally
if (error) {
  console.error('Fatal error:', error);
  process.exitCode = 1;
  return; // or throw error in async context
}

// ✅ Correct in CLI context: Use proper shutdown
async function shutdown(code = 0) {
  await cleanup();
  process.exit(code);
}

// ⚠️ Warning: Synchronous file operation
const fs = require('fs');
const data = fs.readFileSync('data.txt', 'utf8');
const files = fs.readdirSync('./uploads');
const stats = fs.statSync('package.json');

// ✅ Better: Use async versions with async/await
const fs = require('fs').promises;

async function loadData() {
  const data = await fs.readFile('data.txt', 'utf8');  
  const files = await fs.readdir('./uploads');
  const stats = await fs.stat('package.json');
  return { data, files, stats };
}

// ✅ Also correct: Use callback versions
const fs = require('fs');

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

// ✅ Acceptable: Sync operations in startup/initialization code
// (where blocking is acceptable)
const config = JSON.parse(fs.readFileSync('config.json', 'utf8'));

// ✅ Allowed in Node.js config (disabled rule)
import fs from 'fs';
import path from 'path';
import http from 'http';
import crypto from 'crypto';
import { promisify } from 'util';

// CommonJS also allowed
const fs = require('fs');
const path = require('path');

// ✅ Available globals (no-undef won't flag these)
console.log(global);        // Global namespace object
console.log(process);       // Process object
console.log(Buffer);        // Buffer constructor
console.log(__dirname);     // Current directory path
console.log(__filename);    // Current file path

// Timer functions
setImmediate(callback);
clearImmediate(immediateId);

// ✅ CommonJS globals available
console.log(module);        // Current module object
console.log(exports);       // Module exports object
console.log(require);       // Module require function

// Module properties and methods
console.log(module.filename);
console.log(module.id);
console.log(require.resolve('./module'));

// ✅ Proper async error handling
async function processFile(filename) {
  try {
    const data = await fs.readFile(filename, 'utf8');
    return JSON.parse(data);
  } catch (error) {
    // Log and re-throw or handle appropriately
    console.error(`Failed to process ${filename}:`, error.message);
    throw error;
  }
}

// ✅ Callback error handling
function processFile(filename, callback) {
  fs.readFile(filename, 'utf8', (err, data) => {
    if (err) {
      return callback(err);
    }
    
    try {
      const result = JSON.parse(data);
      callback(null, result);
    } catch (parseError) {
      callback(parseError);
    }
  });
}

const path = require('path');

// ✅ Cross-platform path operations
const configDir = path.join(__dirname, 'config');
const logFile = path.resolve(process.cwd(), 'logs', 'app.log');
const extension = path.extname(__filename);
const basename = path.basename(__filename, '.js');

npm install --save-dev eslint-config-recommended

# .eslintrc.yaml
extends:
  - recommended/node

npm install --save-dev eslint-config-node

# .eslintrc.yaml
extends:
  - node