TypeScript Best Practices Skill

TypeScript Best Practices

Comprehensive guide to writing clean, type-safe, and maintainable TypeScript code.

When to Use

Configuring a new TypeScript project
Deciding between interface vs type alias
Writing async/await code
Reviewing TypeScript code quality
Avoiding common TypeScript pitfalls

Quick Reference

// Type inference - let TS do the work
const name = 'Alice';

// Explicit for APIs
function greet(name: string): string { ... }

// Unknown over any
function safe(data: unknown) { ... }

// Type-only imports
import type { User } from './types';

// Const assertions
const tuple = [1, 2] as const;

// Null safety
const len = str?.length ?? 0;

// Guard clauses
if (!valid) throw new Error();
// main logic...

Common Mistakes

| Mistake | Problem | Solution | |---------|---------|----------| | Overusing any | Defeats type checking | Use unknown, generics, or proper types | | Not using strict mode | Misses many errors | Enable "strict": true | | Redundant annotations | Clutters code | Trust type inference | | Ignoring union types | Runtime errors | Use type guards | | Not handling null | Crashes | Use ?. and ?? operators | | Nested conditionals | Hard to read | Use guard clauses | | Duplicate types with Zod | Maintenance burden | Infer from z.infer<typeof schema> | | Sequential awaits for independent ops | Slower execution | Use Promise.all | | Non-Error cause | Breaks error chains | Always use Error instance for cause |

Progressive Disclosure

| Topic | File | When to Use | |-------|------|-------------| | Type system & functions | context/code-patterns.md | Interface vs type, async patterns, guard clauses | | Project structure | context/organization.md | File naming, barrel files, configuration | | Testing & performance | context/testing-performance.md | DI, type guards, null handling, performance |

Key Principles

Type inference when obvious - Let TypeScript infer simple types
Explicit for public APIs - Document function signatures clearly
Unknown over any - Use unknown with type guards instead of any
Guard clauses - Early returns reduce nesting
Type-only imports - Better tree-shaking with import type

Agent Skills: TypeScript Best Practices

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