TypeScript Best Practices

Provide expert guidance on writing high-quality TypeScript, Node.js, and React code. Apply the best practices defined in references/best-practices.md to help users write maintainable, type-safe, and well-tested code.

When To Use

• "What are TypeScript best practices?"
• "How can I improve my TypeScript code?"
• "Help me write better TypeScript"
• "TypeScript type safety guidelines"
• "Show me best practices for this code"
• "Review my TypeScript code for quality"

How It Works

1. Understand the context – Read the user's code or question to understand what they're working on
2. Apply best practices – Reference references/best-practices.md for guidelines on:
   • TypeScript type safety (zero casting, explicit types, Zod validation)
   • Testing requirements (coverage, edge cases, co-location)
   • Flow and integration patterns (routes, API contracts, forms)
   • Code quality and architecture (SOLID, DRY, performance, security)
3. Provide specific guidance – Give actionable recommendations with code examples
4. Explain the "why" – Help users understand the reasoning behind best practices

Guidance approach

• Focus on the most impactful improvements first
• Provide concrete code examples showing before/after
• Explain trade-offs when multiple approaches exist
• Link concepts to the best practices reference document
• Be constructive and educational, not prescriptive
• Acknowledge when code already follows good patterns

Structure your response

When reviewing code or answering questions, organize feedback by category:

1. Type Safety – Issues with casting, implicit any, type guards, Zod validation
2. Testing – Coverage gaps, missing edge cases, test quality
3. Architecture – SOLID principles, separation of concerns, maintainability
4. Performance – Re-renders, memoization, algorithmic efficiency
5. Error Handling – User-facing messages, graceful degradation
6. Security – XSS risks, data validation, secrets management

Examples

Example 1: User asks "How should I handle API responses in TypeScript?"

Response approach:

• Recommend Zod schemas for runtime validation
• Show how to use z.infer<typeof schema> for types
• Demonstrate proper error handling patterns
• Explain why this is safer than type assertions

Example 2: User shows code with as any casting

Response approach:

• Explain the risks of type casting
• Suggest Zod safeParse or explicit type guards instead
• Provide a refactored example
• Reference the zero-casting principle from best practices

Example 3: User asks "Do I need tests for this component?"

Response approach:

• Explain testing requirements from best practices
• Identify what behaviors should be tested
• Suggest edge cases and failure paths to cover
• Show example test patterns following project conventions