Docs: Add section to Effects with guidance on which operator to use

[brandonroberts]

Other information:

Provide some clear documentation on which flattening operator to use for common tasks with Effects. There's 4 to choose from currently.

• concatMap
• exhaustMap
• mergeMap
• switchMap

May could include an example of how each operator behaves differently.

[alex-okrushko]

This article from @cartant can be also linked there: https://ncjamieson.com/avoiding-switchmap-related-bugs/

[jordanpowell88]

I'll work on this

[timdeschryver]

@jordanpowell88 before you do, please check with @brandonroberts .
He might be working on this 😅

[jordanpowell88]

Ok, certainly @brandonroberts will do an excellent job writing this up

[david-shortman]

I'm up for working on this if it's not active

[Armenvardanyan95]

If this is still relevant, I can write a section on this

[brandonroberts]

Thanks @Armenvardanyan95, I'm still planning to take this one

[KylerJohnsonDev]

This is one of the most common issues I see with the implementation of NgRx. People tend to use switchMap even for database writes and, under the right circumstances, it causes subtle issues. @brandonroberts are you still planning to work on this? I'd be happy to take a crack at it.

[tujlaky]

Can someone help me why switchMap is back in the documentation? Is it okay to use or we should avoid it still?

Or what changed that previously it was not added and now back in the doc?

[david-shortman]

switchMap is fine in many circumstances. Picking "flattening operators" is about deciding: "What should happen if a second action comes in while the first is still processing?"

Then follow this flow:

"I only want the result of the latest one and don't care about handling the old one"
→ switchMap (search bars, loading current state)

"I want to handle ALL of them and don't care about order"
→ mergeMap (loading multiple independent things)

"I need to process them one at a time, in incoming order"
→ concatMap (saving data, ordered updates)

"I want to ignore new ones until current one finishes"
→ exhaustMap (submit buttons, login)