TypeScript is structurally typed, so `string` and `string` are interchangeable even when they semantically aren't (UserId vs PostId). The "brand" trick adds a phantom property that exists only at compile time, giving you nominal-ish typing.
TypeScript
type Brand<T, B> = T & { readonly __brand: B };
type UserId = Brand<string, 'UserId'>;
type PostId = Brand<string, 'PostId'>;
const asUserId = (s: string): UserId => s as UserId;
const asPostId = (s: string): PostId => s as PostId;
function deleteUser(id: UserId) { /* ... */ }
const u = asUserId('abc');
const p = asPostId('xyz');
deleteUser(u); // ✓
deleteUser(p); // ✗ Type 'PostId' is not assignable to 'UserId'
deleteUser('raw'); // ✗ raw strings rejectedSave your own code snippets
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