4 RxJS Operators you should know to get last emitted value from observable

Getting the last emitted value from an observable is a common requirement when working with reactive programming in JavaScript. However, it can be challenging to determine which RxJS operators to use to achieve this goal. In this tutorial, I'll cover four essential RxJS operators that you should know to get the last emitted value from an observable. This tutorial is perfect for developers of all levels who want to improve their reactive programming skills and become more efficient at handling asynchronous data streams.

In RxJS, you can use the last() operator to get the last emitted value from an observable. The last() operator emits only the last value from the source observable that meets a specified condition.

last() operator

For example, to get the last emitted value from an observable source$ you can use the following code:

If you want to get the last emitted value that meet some condition:

takeLast(1) operator

You can also use the takeLast(1) operator to get the last emitted value from an observable. This operator emits the last n values from the source observable.

reduce() operator

Alternatively you can use reduce operator, to get the last emitted value from an observable by reducing the emitted values to a single value:

Example:

BehaviorSubject

If you want to get the last value emitted while the observable is still active, you can use the BehaviorSubject which will always hold the last emitted value and will emit that value to new subscribers.

Example:

Keep in mind that these operators will only return the last emitted value at the time the subscription is made, if you want to keep track of the last emitted value each time the observable emits a new value you need to use a BehaviorSubject or ReplaySubject which stores the last emitted value and emits it to new subscribers.

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