When nothing comes in RxJS
RxJS interview exercise on Errors & completion, 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.
Write requireSome(source$), which errors with the message "No values" when the source completes without emitting, and orDefault(source$, value), which emits `value` in that case. Sources that emit are passed through unchanged.
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.