Nodejs

# Node.js Error Patterns Common Node.js errors with diagnosis and solutions. ## Module Errors ### MODULE_NOT_FOUND ``` Error: Cannot find module 'package-name' ``` **Causes**: 1. Package not installed 2. Typo in import/require 3. node_modules corrupted 4. Wrong relative path **Solutions**: ```bash # Install missing package npm install package-name # If corrupted node_modules rm -rf node_modules package-lock.json npm install # Check if package exists npm ls package-name ``` **Prevention**: Use `npm ci` in CI/CD, add postinstall check. --- ### ERR_MODULE_NOT_FOUND (ESM) ``` Error [ERR_MODULE_NOT_FOUND]: Cannot find package 'x' imported from y ``` **Causes**: 1. ESM import without file extension 2. Package doesn't support ESM 3. Missing `"type": "module"` in package.json **Solutions**: ```javascript // Add file extension for local imports import { foo } from './utils.js' // Not './utils' // For CommonJS packages, use createRequire import { createRequire } from 'module' const require = createRequire(import.meta.url) const pkg = require('commonjs-package') ``` --- ## Network Errors ### ECONNREFUSED ``` Error: connect ECONNREFUSED 127.0.0.1:3000 ``` **Causes**: 1. Server not running 2. Wrong port 3. Firewall blocking **Diagnosis**: ```bash # Check if port is in use lsof -i :3000 netstat -an | grep 3000 # Check if service is running ps aux | grep node ``` **Solutions**: 1. Start the server first 2. Verify port number matches 3. Check firewall rules --- ### ENOTFOUND ``` Error: getaddrinfo ENOTFOUND hostname ``` **Causes**: 1. Invalid hostname/URL 2. DNS resolution failure 3. No internet connection **Diagnosis**: ```bash # Test DNS resolution nslookup hostname dig hostname # Test connectivity ping hostname curl -I https://hostname ``` **Solutions**: 1. Check URL spelling 2. Try IP address instead of hostname 3. Check /etc/hosts file 4. Check DNS settings --- ### ETIMEDOUT ``` Error: connect ETIMEDOUT ``` **Causes**: 1. Network too slow 2. Server overloaded 3. Firewall silently dropping **Solutions**: ```javascript // Increase timeout const axios = require('axios') axios.get(url, { timeout: 30000 }) // With fetch const controller = new AbortController() setTimeout(() => controller.abort(), 30000) fetch(url, { signal: controller.signal }) ``` --- ## File System Errors ### ENOENT ``` Error: ENOENT: no such file or directory, open 'path/to/file' ``` **Causes**: 1. File doesn't exist 2. Wrong path (relative vs absolute) 3. Typo in filename **Diagnosis**: ```bash # Check if file exists ls -la path/to/file # Check current working directory pwd # List directory contents ls -la path/to/ ``` **Solutions**: ```javascript // Check before accessing const fs = require('fs') if (fs.existsSync(filePath)) { // proceed } // Use path.join for cross-platform const path = require('path') const filePath = path.join(__dirname, 'data', 'file.json') ``` --- ### EACCES ``` Error: EACCES: permission denied ``` **Causes**: 1. No read/write permission 2. File owned by another user 3. Directory not accessible **Diagnosis**: ```bash # Check permissions ls -la /path/to/file # Check ownership stat /path/to/file ``` **Solutions**: ```bash # Change permissions (careful!) chmod 644 /path/to/file # read/write for owner, read for others chmod 755 /path/to/dir # execute for directories # Change ownership sudo chown $USER:$USER /path/to/file # For npm global packages sudo chown -R $USER /usr/local/lib/node_modules ``` --- ### EMFILE ``` Error: EMFILE: too many open files ``` **Causes**: 1. Opening files without closing 2. System file descriptor limit reached 3. Watching too many files **Solutions**: ```bash # Check current limit ulimit -n # Increase limit (temporary) ulimit -n 10000 # Increase limit (permanent) - add to ~/.bashrc or /etc/security/limits.conf # * soft nofile 10000 # * hard nofile 10000 ``` ```javascript // Use streams for large files const stream = fs.createReadStream(file) stream.on('close', () => { // file handle released }) // Use graceful-fs const fs = require('graceful-fs') ``` --- ## Syntax/Parse Errors ### SyntaxError: Unexpected token ``` SyntaxError: Unexpected token '<' ``` **Common Causes by Token**: | Token | Likely Cause | |-------|--------------| | `<` | HTML returned instead of JSON (API error, 404 page) | | `}` | Missing opening brace or extra closing | | `{` | Missing closing brace | | `)` | Missing opening parenthesis | | `import` | Using ESM in CommonJS context | | `await` | await outside async function | **Solutions**: ```javascript // For ' {}) .catch(error => console.error(error)) // Or use try/catch with async/await async function main() { try { const result = await someAsyncOperation() } catch (error) { console.error('Error:', error) } } // Global handler (last resort) process.on('unhandledRejection', (reason, promise) => { console.error('Unhandled Rejection:', reason) }) ``` --- ### ERR_INVALID_CALLBACK ``` TypeError [ERR_INVALID_CALLBACK]: Callback must be a function ``` **Causes**: 1. Passing non-function where callback expected 2. Missing callback argument 3. Mixing callback and promise APIs **Solutions**: ```javascript // Wrong - mixing styles fs.readFile('file.txt', 'utf8') // Missing callback // Correct - callback style fs.readFile('file.txt', 'utf8', (err, data) => { if (err) throw err console.log(data) }) // Correct - promise style const fs = require('fs').promises const data = await fs.readFile('file.txt', 'utf8') ``` --- ## Memory Errors ### JavaScript heap out of memory ``` FATAL ERROR: CALL_AND_RETRY_LAST Allocation failed - JavaScript heap out of memory ``` **Causes**: 1. Memory leak 2. Processing large data in memory 3. Infinite loop creating objects **Solutions**: ```bash # Increase memory limit node --max-old-space-size=4096 app.js # For npm scripts NODE_OPTIONS="--max-old-space-size=4096" npm run build ``` ```javascript // Use streams for large files const stream = fs.createReadStream('large-file.json') stream.on('data', chunk => { // Process chunk by chunk }) // Clear references let data = loadLargeData() processData(data) data = null // Allow garbage collection ``` **Diagnosis**: ```javascript // Monitor memory usage setInterval(() => { const used = process.memoryUsage() console.log(`Memory: ${Math.round(used.heapUsed / 1024 / 1024)}MB`) }, 5000) ``` --- ## Process Errors ### SIGTERM / SIGINT ``` Process exited with SIGTERM ``` **Causes**: 1. Process killed externally (Ctrl+C, kill command) 2. Container orchestrator stopping container 3. System shutdown **Solutions**: ```javascript // Graceful shutdown process.on('SIGTERM', () => { console.log('SIGTERM received, shutting down gracefully') server.close(() => { console.log('Server closed') process.exit(0) }) }) process.on('SIGINT', () => { console.log('SIGINT received (Ctrl+C)') process.exit(0) }) ``` --- ## NPM Errors ### ERESOLVE unable to resolve dependency tree ``` npm ERR! ERESOLVE unable to resolve dependency tree ``` **Causes**: 1. Peer dependency conflict 2. Package version mismatch 3. npm 7+ stricter resolution **Solutions**: ```bash # See the conflict npm install --legacy-peer-deps # Or force install (use carefully) npm install --force # Better: fix the conflict npm ls package-name # See which versions are installed npm why package-name # See why it's installed ``` --- ### EINTEGRITY ``` npm ERR! EINTEGRITY sha512-xxx ``` **Causes**: 1. Corrupted cache 2. Package modified after caching 3. Network issues during download **Solutions**: ```bash # Clear npm cache npm cache clean --force # Remove and reinstall rm -rf node_modules package-lock.json npm install ``` --- ## Quick Reference Table | Error Code | Category | Quick Fix | |------------|----------|-----------| | `MODULE_NOT_FOUND` | Dependency | `npm install ` | | `ECONNREFUSED` | Network | Start the server | | `ENOTFOUND` | Network | Check URL/hostname | | `ENOENT` | Filesystem | Check file path exists | | `EACCES` | Permission | `chmod` or `chown` | | `EMFILE` | Filesystem | Increase ulimit | | `heap out of memory` | Memory | `--max-old-space-size` | | `Unexpected token` | Syntax | Check file content type | | `not a function` | Type | Check import/export | | `ERESOLVE` | NPM | `--legacy-peer-deps` |