Context with a hook in React
React interview exercise on Context & reducers, 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 ThemeProvider({ theme, children }) providing "light" or "dark", useTheme() returning it (throwing "useTheme needs a ThemeProvider" without one), and ThemedButton({ children }), a <button> with the class "btn-light" or "btn-dark".
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.