Heldinhow/typescript-patterns

TypeScript Design Patterns

Overview

TypeScript design patterns apply established software design principles within the TypeScript type system to create maintainable, reusable, and type-safe code. This skill should be invoked when writing TypeScript code requiring best practices, building reusable libraries, or creating well-typed application architectures.

Core Principles

• Type Safety: Leverage TypeScript's static typing to catch errors at compile time
• Generics: Write reusable code that works with any type
• Structural Typing: Use interface composition over inheritance
• Utility Types: Leverage built-in utility types (Partial, Pick, Omit, etc.)

Preparation Checklist

• [ ] Enable strict mode in tsconfig.json
• [ ] Plan type hierarchy for your domain
• [ ] Identify opportunities for generics
• [ ] Define error handling strategy

Step-by-Step Process

1. Define Types: Create interfaces and types for domain models
2. Apply Generics: Refactor repetitive code into generic functions/classes
3. Use Composition: Build complex types from simpler ones
4. Handle Errors: Create discriminated unions for error handling
5. Leverage Utilities: Use Partial, Pick, Omit for type transformations
6. Validate: Ensure strict mode catches all type errors

Do's and Don'ts

• ✅ Do enable strict mode in TypeScript config
• ✅ Do use discriminated unions for error handling
• ✅ Do prefer interfaces for object shapes, types for unions
• ❌ Don't use any - it defeats TypeScript's purpose
• ❌ Don't over-engineer simple scripts with complex generics
• ❌ Don't ignore generic constraints when needed

Anti-Patterns

• Any Abuser: Using any to bypass type checking
• Type Ignorance: Not leveraging TypeScript's inference
• Over-Generics: Creating complex generic types that are hard to read
• No Strictness: Disabling strict checks that catch real bugs