In TypeScript, both interface and type allow you to define the shape of data, but they serve slightly different purposes.
Use interface when:
- Defining the structure of objects or classes.
- You want to allow extension via declaration merging.
- You need a contract that classes can implement.
Use type when:
- Defining unions, intersections, tuples, or primitives.
- Creating quick type aliases beyond just object shapes.
- You want to combine multiple types with intersections.
Key difference: Interfaces support declaration merging and are ideal for object contracts, while type aliases offer more flexibility for complex types.
In short, use interfaces for object-oriented design and extendable APIs, and type aliases for more advanced or composite types.
Both are erased at compile time, so there’s no runtime cost just pick the right tool for clarity and maintainability.
Thanks.