Understanding the Difference Between Interface and Type in TypeScript: When to Use Each

When working with TypeScript, developers often encounter two ways to define shapes for objects: interface and type . While they can look similar, there are important differences and best-use cases. Key Differences Extensibility : interface can be extended multiple times by declaration merging or by using the extends keyword. type is closed after its definition. You can't merge or reopen a type , but you can create new types by intersecting them. Declaration : Use interface for defining the shape of objects, especially when you expect the structure to grow. Use type for composing types, unions, primitives, and tuples. Implements : Classes can implement both interfaces and types, but interfaces work more naturally with class implementation. Union and Intersection : Only type can create union types ( type AorB = A | B ) and intersection types ( type AB = A & B ). Examples Interface Example interface User { name : string ; age : number ; } interface User { email : string ; } // Merged into