merge and concat in RxJS
RxJS interview exercise on Combining, 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 interleave(a$, b$), which emits from both sources as values arrive, and oneAfterAnother(a$, b$), which emits all of a$ and only then subscribes to b$. Both complete when everything has completed.
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.