[Angular] State provider solutions

There are many ways to expose data to components, but based on different usecase, different solution has PROS & CONS.

1. ShareReplay(1)

PROS: ShareReplay(1) solves a problem which if you have multi subscribers, it will trigger API requests multi times if you don't have shareReplay(1) in place.

CONS: data is static, not dynamic. If you want to add/remove/update the data, you have to fetch new data again.

2. Subject as a service

We can keep a local copy of data using BehaviorSubject. Everytime, we add/remove/update, will trigger subject update.

PROS: Solve the problem for static data, now it is dynamic and it won't trigger multi API calls.

CONS: It has race condition. If you try to add multi-times. it might happne that first request's response comes after second request's response. 

3. NgRx (ComponentStroe)

https://ngrx.io/guide/component-store

ComponentStore vs Global store: https://ngrx.io/guide/component-store/comparison

We need state for some components, it is not necessary add to global store.

PROS: It handles race condition by using effect (you can define your approach by using concatMap, switchMap, mergeMap, exhaustMap)

concatMap: is a good way to solve race condition.

switchMap: only care new request, ignore old one

exhaustMap: only care the current happening one,  ignore new ones during the period

Performance it better, NgRx using select() with memorized function.

CONS: Deep knowledge of RxJS and NgRx.

Misc:

tapResponse:

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 Refer: 

Filling the Gap in State with NgRx ComponentStore | Alex Okrushko | EnterpriseNG 2020