State with a BehaviorSubject in RxJS

RxJS interview exercise on Subjects & sharing, difficulty 2 of 3. Solve it in the editor beside a worked example; the tests run the moment you do.

Write Store<T>: constructed with an initial state; `state emits the current state to every subscriber at once and…" /> emits the current state to every subscriber at once and…" /> emits the current state to every subscriber at once and…" /> emits the current state to every subscriber at once and…" /> emits the current state to every subscriber at once and…" /> emits the current state to every subscriber at once and…" /> emits the current state to every subscriber at once and…" /> emits the current state to every subscriber at once and then every change; get() returns the current state; update(fn) replaces it with fn(current); select(key) emits state[key] now and whenever it changes, skipping emissions where it did not change.

Each exercise pairs a worked example with a twin problem to solve in a real editor; the tests run the moment you do. Progress is saved in your browser, and in your account if you sign in.

More Subjects & sharing in RxJS

• A Subject as an event bus
• The last few, for latecomers
• One source, many subscribers
• A custom operator

All RxJS exercises · Other languages and frameworks