RxJS Interview Questions and Answers
Experienced / Expert level questions & answers
Ques 1. Explain the concept of multicasting in RxJS.
Multicasting is the process of broadcasting a single source Observable to multiple subscribers, preventing redundant work for shared operations.
Example:
const subject = new Subject(); observable.subscribe(subject);
Ques 2. What is the difference between 'Cold' and 'Hot' Observables?
'Cold' Observables start producing values only when a subscription is made, while 'Hot' Observables produce values even before any subscriptions.
Example:
Cold: const coldObservable = new Observable(...); Hot: const hotObservable = new Subject();
Ques 3. Explain the purpose of the 'debounceTime' operator in RxJS.
The 'debounceTime' operator is used to emit a value from an Observable only after a specified amount of time has passed without any new values being emitted.
Example:
const debouncedObservable = inputObservable.pipe(debounceTime(300));
Ques 4. Explain the concept of 'Schedulers' in RxJS.
Schedulers are used to control the execution context and timing of Observable operations, allowing you to control when and where certain code is executed.
Example:
const scheduledObservable = observable.pipe(delay(1000, asyncScheduler));
Ques 5. What is the purpose of the 'finalize' operator in RxJS?
'finalize' is used to perform a specified action when an Observable completes, whether it completes normally or due to an error.
Example:
const finalizedObservable = observable.pipe(finalize(() => console.log('Observable completed')));
Ques 6. Explain the concept of 'ReplaySubjects' in RxJS.
ReplaySubjects are similar to Subjects but can 'replay' a specified number of previously emitted values to new subscribers, ensuring they receive a specific history of values.
Example:
const replaySubject = new ReplaySubject(2); replaySubject.next('First value'); replaySubject.next('Second value'); replaySubject.subscribe(value => console.log(value));
Ques 7. Explain the difference between 'BehaviorSubjects' and 'ReplaySubjects' in RxJS.
BehaviorSubjects always emit the latest value to new subscribers, while ReplaySubjects can replay a specified number of previous values to new subscribers.
Example:
const behaviorSubject = new BehaviorSubject('Initial value'); behaviorSubject.next('Updated value'); behaviorSubject.subscribe(value => console.log(value));
Ques 8. What is the purpose of the 'debounce' operator in RxJS?
'debounce' is used to discard values emitted by an Observable that follow each other too quickly, allowing only the last value within a specified time window to be emitted.
Example:
const debouncedObservable = inputObservable.pipe(debounce(() => timer(300)));
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