The last few, for latecomers in RxJS
RxJS interview exercise on Subjects & sharing, 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 RecentLog(keep): add(line) records a line; lines$ gives each new subscriber the last `keep` lines already recorded, in order, and then every new one. Before anything was added a subscriber simply waits.
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.