Answer
Subject: No initial value; subscribers only receive future values.
BehaviorSubject: Has initial value and gives latest value to new subscribers.
ReplaySubject: Stores a buffer of values and replays them to new subscribers.
Quick Answer
Subject: both Observable and Observer - can emit values and subscribe. Used for custom events. BehaviorSubject: remembers and replays the last value to new subscribers, requires initial value - use for current state (like selectedUser$). ReplaySubject: replays N last values to new subscribers - use when late subscribers need history. All are multicast - multiple subscribers share one execution.
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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