Keys that keep state where it belongs in React
React interview exercise on Performance, difficulty 2 of 3. Solve it in the editor beside a worked example; the tests run the moment you do.
Guests renders one row per guest ({ id, name }): the name and an <input className="seat"> where the host types a seat number (uncontrolled is fine). A <button className="sort"> sorts the guests by name. Seat numbers already typed must stay with their guest after sorting.
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.