Generic groupBy in TypeScript
TypeScript interview exercise on TypeScript, difficulty 3 of 3. Solve it in the editor beside a worked example; the tests run the moment you do.
Write a generic groupBy<T, K extends string>(items: T[], key: (item: T) => K): Record<K, T[]>.
Each exercise pairs a worked example with a twin problem to solve in a real editor; the tests run the moment you do. Progress is saved in your browser, and in your account if you sign in.