JavaScript Best Practices

Comprehensive coding standards for JavaScript development, optimized for AI agents and LLMs. Contains 24 rules across 8 categories, prioritized by impact.

When to Apply

Reference these guidelines when:

• Writing vanilla JavaScript code
• Implementing async operations and promises
• Handling DOM manipulation
• Optimizing JavaScript performance
• Reviewing code for security issues
• Working with ES modules and modern features

Rule Categories by Priority

Quick Reference

1. Performance (CRITICAL)

• perf-avoid-memory-leaks - Clean up event listeners and intervals
• perf-dom-batch-updates - Batch DOM updates with DocumentFragment
• perf-debounce-throttle - Debounce scroll/resize handlers
• perf-avoid-layout-thrashing - Separate reads and writes to DOM
• perf-web-workers - Use Web Workers for heavy computation

2. Async Patterns (CRITICAL)

• async-promise-all - Use Promise.all() for parallel operations
• async-promise-allsettled - Use allSettled() when some can fail
• async-error-boundaries - Handle promise rejections properly
• async-avoid-nested-promises - Flatten with async/await
• async-cancellation - Use AbortController for cancellable requests

3. Security (HIGH)

• security-no-innerhtml - Use textContent instead of innerHTML
• security-no-eval - Never use eval() or new Function()
• security-sanitize-user-input - Sanitize before DOM insertion
• security-csp-compliance - Write CSP-compliant code

4. Error Handling (HIGH)

• error-custom-errors - Create custom Error classes
• error-async-try-catch - Wrap async operations in try-catch
• error-global-handler - Implement window.onerror handler

5. ES Modules (MEDIUM-HIGH)

• module-named-exports - Prefer named exports for tree-shaking
• module-barrel-files - Avoid barrel files in performance-critical code
• module-dynamic-imports - Use dynamic imports for code splitting

6. Data Structures (MEDIUM)

• data-map-over-object - Use Map for dynamic key collections
• data-set-for-uniqueness - Use Set for unique value collections
• data-immutable-updates - Use spread operator for immutability

7. Modern Features (LOW-MEDIUM)

• modern-optional-chaining - Use ?. for safe property access

How to Use

Read individual rule files for detailed explanations and code examples.

Full Compiled Document

For the complete guide with all rules expanded: AGENTS.md