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Frontend question · TypeScript › Types vs interfaces

Which version compiles?

// Version A
interface User { id: string }
interface User { name: string }
const u: User = { id: "1", name: "Ann" };

// Version B
type Account = { id: string };
type Account = { name: string };
Only Version A

Only Version A compiles. Interfaces with the same name merge into one, so User has both id and name.

"Both" is wrong because type aliases cannot be declared twice. Version B fails with a "Duplicate identifier" error.