Syncing with the outside: useEffect in React
React interview exercise on Effects & refs, difficulty 1 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.
Write DocumentTitle with a `title` prop: it sets document.title to "<title> · Shop" whenever the title changes and restores the previous document title when it unmounts. It renders nothing.
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.