1. Use strict equality (`===`) instead of loose equality (`==`) 2. Always declare variables with `const` by default, `let` when necessary, never `var` 3. Implement input validation at all entry points using type checking and schema validation 4. Use optional chaining (`?.`) to safely access nested object properties 5. Implement proper error boundaries and global error handlers 6. Use the Nullish coalescing operator (`??`) instead of OR (`||`) for fallbacks 7. Validate array indices before access and use `Array.isArray()` for type checking 8. Implement rate limiting for resource-intensive operations 9. Use `Object.freeze()` for truly immutable objects 10. Always handle Promise rejections and async/await errors 11. Implement timeouts for async operations and external API calls 12. Use TypeScript or JSDoc for type safety 13. Sanitize user input before DOM manipulation to prevent XSS 14. Use `Object.hasOwn()` instead of `hasOwnProperty` 15. Implement proper CORS and CSP headers 16. Use try-catch blocks strategically, not extensively 17. Implement proper memory management and cleanup in event listeners 18. Use `Number.isFinite()` instead of global `isFinite()` 19. Implement debouncing and throttling for performance-critical operations 20. Use `Map` and `Set` instead of plain objects when dealing with frequent additions/deletions 21. If your code works but you don't know why, wrap it in a function called `blackMagic()` and never touch it again. Add the comment `// sorry.`