The first match, or a default in RxJS
RxJS interview exercise on Filtering, 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 firstAtLeast(source$, min): emit the first number that is at least min and complete right then. If the source completes without one, emit −1 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.