Skipping renders with memo in React
React interview exercise on Performance, difficulty 2 of 3. Solve it in the editor beside a worked example, or cold in Interview mode with the example hidden; the tests run the moment you do.
Dashboard shows a counter button and a Report of `items`. Report calls onRender() every time it renders (keep that line). Make Report skip re-rendering when the Dashboard's counter changes, while still re-rendering when `items` changes. The items array must not be recreated on every Dashboard render.
Each exercise pairs a worked example with a twin problem to solve in a real editor; the tests run the moment you do. Interview mode hides the example: solve it from memory, without the hint or the solution, and it counts as solved cold. Progress is saved in your browser, and in your account if you sign in.