Why does concatMap((x) => x) work the same as concatMap((x) => from(x))?

[ilyakonrad]

I am trying to understand the behavior of concatMap().
Specifically the case when the projection function returns its argument as is. In my case it's an array.
I am trying to figure out why concatMap() transforms emitted value (an array) into separate emissions of every item of the array.

Here's the setup:

const source$ = of([1, 2, 3])

const resultConcat$ = source$.pipe(concatMap((x) => {
  console.log(x); // [1, 2, 3]
  return x
}))

resultConcat$.subscribe((value) => console.log(value))

// result:
// 1
// 2
// 3

It works the same when instead of doing return x I do return from(x).
But then it makes sense, because from() is supposed to emit items of the array separately.

What am I missing?

[demensky]

If you put a breakpoint inside the project function and then navigate up you will see from there.
The example is shown in code from the master branch. But on the version that you use, the essence is about the same.

So yes, you don't need to use from in places where the type is specified as ObservableInput (which includes ArrayLike<T> and Iterable<T>).

[ilyakonrad]

Going up while debugging didn't get me to it, but I checked the source code and I got it.
I wonder why it's not clear from the documentation though.
Thank you for helping!

[jakovljevic-mladen]

There are known issues with the docs related to the ObservableInput parameters. We have a plan to update the documentation, we're sorry this has caused issues for you.