TypeScript Interfaces vs Types

Both interfaces and type aliases define object shapes, but they have key differences. Here's when to use each.

Best Practices#

Use Interface When:
✓ Defining object shapes
✓ Creating public APIs
✓ Need declaration merging
✓ Implementing in classes

Use Type When:
✓ Creating union types
✓ Working with primitives
✓ Using mapped/conditional types
✓ Creating type utilities

General Guidelines:
✓ Be consistent in your codebase
✓ Interface for objects, type for everything else
✓ Document complex types
✓ Prefer interface for public APIs

Avoid:
✗ Mixing without reason
✗ Over-engineering types
✗ Ignoring readability
✗ Complex nested intersections

Both interfaces and types are powerful tools. Use interfaces for object shapes, class contracts, and public APIs. Use types for unions, primitives, tuples, and advanced type operations. For simple object types, either works - just be consistent. When in doubt, start with interface and switch to type if you need its unique features.

TypeScript Interfaces vs Types

Basic Syntax#

Extension#

Declaration Merging#

Augmenting Libraries#

Primitive Types#

Union and Intersection#

Functions#

Classes#

Generics#

Recursive Types#

Performance#

Error Messages#

When to Use Each#

Best Practices#

Conclusion#

Share this article

Related articles

TypeScript Interface vs Type

Advanced TypeScript Patterns for Production Code

TypeScript Type Inference Guide