Answer
BehaviorSubject stores the latest value and immediately emits it to subscribers—ideal for UI and state.
ReplaySubject replays a buffer of previous values—ideal for logs, history, or cached responses.
Quick Answer
BehaviorSubject: requires initial value, replays the LAST value to new subscribers - perfect for current state (currentUser$, selectedTab$). ReplaySubject(n): replays last N values to new subscribers - useful when late subscribers need some history. BehaviorSubject is the most common for state sharing in Angular services. ReplaySubject(1) is similar to BehaviorSubject but without mandatory initial value.
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SugharaIQ Editorial Team
Verified Answer
This answer has been peer-reviewed by industry experts holding senior engineering roles to ensure technical accuracy and relevance for modern interview standards.
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Source: SugharaIQ