RxJs: conditional mergeMap in pipe?

Question

JavaScript

I have this amazing code:

this.myApi.getSomething(id).pipe(
    shop.isNew
        ? (
              map(tags => ({ ...updatedShop, tags })),
              mergeMap(() =>
                  this.myApi.addTags(updatedShop.id, shop.tags).pipe(
                      map(() => {
                          return {
                              ...updatedShop,
                              tags: shop.tags
                          };
                      })
                  )
              )
          )
        : map(tags => ({ ...updatedShop, tags }))
)

I can’t figure out how to make this work: if the condition is met, call the second service method and run `mergeMap` besides `map`, otherwise - only `map`
is it possible to implement somehow?

Answer 1

// Да, сначала мы делаем map, потому что он делается полюбому:

let doSomething$ = this.myApi.getSomething(id).pipe(
  map(tags => ({ ...updatedShop, tags }))
)

// А затем мы делаем mergeMap если понадобится:

if (shop.isNew) {
  doSomething$ = doSomething$.pipe(
    mergeMap(() =>
                  this.myApi.addTags(updatedShop.id, shop.tags).pipe(
                      map(() => {
                          return {
                              ...updatedShop,
                              tags: shop.tags
                          };
                      })
                  )
              )
  )
}

// ну и затем подписываемся на это дело чтоб оно начало работать:

doSomething$.subscribe();

It will be much easier for you to understand RxJS after watching this video: https://www.youtube.com/watch?v=3LKMwkuK0ZE It is slightly behind the times (operators are now added to the browser via the pipe() function), but the principles themselves described in the video, do not go anywhere.
UPD
If the code above makes you sad, then you can do this:

this.myApi.getSomething(id).pipe(
  map(tags => ({ ...updatedShop, tags })),
  mergeMap((tags) => {
    if (!shop.isNew) {
      return of(tags);
    }
   return this.myApi.addTags(updatedShop.id, shop.tags).pipe(
                      map(() => {
                          return {
                              ...updatedShop,
                              tags: shop.tags
                          };
                      })
                  )
  }),
)

It means that you can take out the if in the mergeMap itself. And if the store is not new, then return the observation from the store, and if it is new, then do something else there.