typescript-interface-vs-type

Use a TypeScript interface for extensible object definitions and declaration merging, while a type alias is better for unions, mapped types, and complex type expressions.

To model API responses in TypeScript, use an interface if you need library compatibility and future declaration merging, or use a type alias for complex expressions and union structures.

TypeScript declaration merging only works with interfaces, allowing multiple same-name interface declarations to combine, whereas type aliases cannot be merged after declaration.

The best way to extend object shapes in TypeScript is using interfaces, which support extending multiple interfaces simultaneously and integrate cleanly with existing library definitions.

TypeScript type aliases are specifically required for creating union types and mapped types, as interfaces cannot express these complex type expressions or conditional type logic.

Library type conflicts often occur when using type aliases instead of interfaces; interfaces support declaration merging to augment existing library definitions without causing naming conflicts.