Wrapping a callback API in RxJS
RxJS interview exercise on Creating observables, 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.
A sensor has start(callback) and stop(). Write watch(sensor): an observable of its readings that calls start when subscribed (each subscriber starts its own) and stop when the subscriber unsubscribes. Nothing must happen before the subscription.
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.