The difference between BehaviorSubject and Observable in Angular and RxJS revolves around their behavior and capabilities in handling data streams.
Observable
An Observable is a foundational concept in RxJS, representing a lazy collection of multiple values over time. Observables are used to handle asynchronous data streams, such as user input, HTTP requests, and other time-based events. They are "cold" by nature, meaning they do not start emitting data until an observer subscribes. Each subscription to an Observable results in an independent execution of the Observable's data-producing function, which can lead to different results for different subscribers[1][2].
BehaviorSubject
BehaviorSubject, on the other hand, is a specialized type of Observable known as a Subject. It has all the characteristics of a standard Observable, but with additional features that make it suitable for specific scenarios. The key feature of BehaviorSubject is that it requires an initial value and stores the current value. This means that upon subscription, BehaviorSubject will emit the most recent value to the subscriber. This is particularly useful in scenarios where you need to ensure that all subscribers receive the most current state, regardless of when they subscribe[1][3].
Key Differences
Initial Value: BehaviorSubject requires an initial value and emits the current value to new subscribers. Regular Observables do not have this feature and only emit values when the data-producing function generates them post-subscription[3].
