Intern / FresherTypeScript
What is the difference between interface and type in TypeScript?
Quick answer
Both describe object shapes. interface can be merged and is preferred for public object contracts; type can express unions, intersections and primitives, and cannot be reopened later.
For a simple object, they look the same and teams pick one style. interface supports declaration merging: two interface User blocks become one, which is how many .d.ts files extend library types. type aliases are fixed once written.
Use type when you need a union (string | number), a mapped type, or a tuple. Use interface when you are describing an object that others might extend. You can implement either with a class. Do not waste interview time claiming one is “faster”; they compile to the same nothing.
interface User { id: string; name: string }
interface User { email?: string } // merged
type Id = string | number; // union: type only
type Admin = User & { role: "admin" }; // intersectionKey points
- interface: extendable, mergeable, object-shaped
- type: unions, intersections, primitives, tuples
- Pick one style for objects and stay consistent