A fallback on error in RxJS
RxJS interview exercise on Errors & completion, 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 orFallback(source$, fallback): pass values through; if the source errors, emit `fallback` once and complete instead of erroring.
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.