typescript.mdc

---
description: TypeScript coding standards and best practices for modern web development
globs: **/*.ts, **/*.tsx, **/*.d.ts
---

# TypeScript Best Practices

## Type System
- Prefer interfaces over types for object definitions
- Use type for unions, intersections, and mapped types
- Avoid using `any`, prefer `unknown` for unknown types
- Use strict TypeScript configuration
- Leverage TypeScript's built-in utility types
- Use generics for reusable type patterns

## Naming Conventions
- Use PascalCase for type names and interfaces
- Use camelCase for variables and functions
- Use UPPER_CASE for constants
- Use descriptive names with auxiliary verbs (e.g., isLoading, hasError)
- Prefix interfaces for React props with 'Props' (e.g., ButtonProps)

## Code Organization
- Keep type definitions close to where they're used
- Export types and interfaces from dedicated type files when shared
- Use barrel exports (index.ts) for organizing exports
- Place shared types in a `types` directory
- Co-locate component props with their components

## Functions
- Use explicit return types for public functions
- Use arrow functions for callbacks and methods
- Implement proper error handling with custom error types
- Use function overloads for complex type scenarios
- Prefer async/await over Promises

## Best Practices
- Enable strict mode in tsconfig.json
- Use readonly for immutable properties
- Leverage discriminated unions for type safety
- Use type guards for runtime type checking
- Implement proper null checking
- Avoid type assertions unless necessary

## Error Handling
- Create custom error types for domain-specific errors
- Use Result types for operations that can fail
- Implement proper error boundaries
- Use try-catch blocks with typed catch clauses
- Handle Promise rejections properly

## Patterns
- Use the Builder pattern for complex object creation
- Implement the Repository pattern for data access
- Use the Factory pattern for object creation
- Leverage dependency injection
- Use the Module pattern for encapsulation