typescript-interface-vs-type

Use interface by default for object type definitions, following the official TypeScript Handbook recommendation. Switch to type only when you need unions, mapped types, conditional types, tuples, or function type aliases.

Interface extends is preferred over the & intersection operator. It raises errors at the definition site for incompatible properties and performs better because interfaces are cached by name while intersections are recomputed on each use.

No, interfaces cannot express union types. Use a type alias for unions such as type Status = 'pending' | 'approved' | 'rejected', as well as for mapped, conditional, and tuple types.

Type intersections defer error detection until the conflicting property is actually accessed, so a definition like Base & { id: string } compiles silently. Interface extends surfaces the incompatibility immediately at the declaration.

Yes, interfaces are cached by name so TypeScript computes the type once and reuses it. Intersections are recomputed every time they are used, which slows type checking in codebases with complex type relationships.