type Identifiable = { id: string | number };
function indexById<T extends Identifiable>(items: readonly T[]): Map<T['id'], T> {
  return new Map(items.map(item => [item.id, item]));
}
const posts = indexById([
  { id: 1, title: 'Hooks' },
  { id: 2, title: 'Generics' },
]);
console.log(posts.get(2)?.title);