None of the guide pages mentions ngModules. Only `observables-in-angular` needed conversion to Standalone.
However, some of the guide pages reflect old versions of RxJS, including signatures that are no longer valid. These have been corrected.
More significantly, *the existing guide is pretty bad at explaining RxJS and its usage*. It was written (by me I think) in the very early days of Angular and Angular RxJS instruction. I've taught numerous "RxJS in Angular" classes since and learned from that experience what does and does not work with students.
There was neither the time nor the charter to completely overhaul this guide. But this commit attempts to remove what flops with students and to bring the teaching closer to what seems more effectively. I hope reviewers agree that my revisions are an improvement.
**Revised Overview**
The overview doc, `observables.md`, had a few errors (ex: `next` is NOT REQUIRED) and deprecated patterns (you now must pass the Observer object to `subscribe`).
More importantly, it was wildly overcomplicated and scary, especially when it got into multi-casting.
Moved the multi-casting section to "RxJS Library" and rewrote it (with working example) for simplicity and context.
I made other changes in an effort to make this an overview that is more comprehensive and more clear. I paid particular attention to the "Basic usage and terms" section.
Finally, I relocated the "Naming conventions for observables" section here from `rx-library`. This is the section that describes the dollar-sign convention. It made more sense for it to be here.
**Revised "RxJS Library" page and code**
*RxJS no longer supports chaining* and hasn't for a very long time. Removed note in `rx-library.md` that suggested you could use operator chaining.
The RxJS `pipe` discussion in the "Operators" section was just weird. Almost no one calls the `pipe` function. We certainly should *start* there. We should start with how people actually use operators - by adding them to the argument list of the `Observable.pipe()` method.
I kept the original `pipe` function example but subordinated it in a "callout". Most readers will (and should) ignore it.
`Subject` is a *critically important RxJS mechanism for creating custom observables*. It was completely missing from the list of observable creators on this guide page. So I added it to the "Observable creation functions" section of the guide and wrote an accompanying `MessageService` code sample (see the new `rx-library/app/` folder).
The `MessageService` is a pretty common pattern in Angular apps - far more common than creating an observable from a counter or an event, two of the creation patterns currently on this page.
This new section also afforded an opportunity to show how RxJS helps with building loosely coupled applications. We will soon be talking about Signals. Many will wonder whether and when they should still use RxJS.
At least a partial answer is that RxJS is really good at progressively combining and enhancing streams of data as they cross component boundaries. Of course you can pass signals around; but they are not as rich in transformers as RxJS. This is where RxJS shines.
**Revised "Comparing observables"**
The Promises section in `comparing-observables.md` had many errors and misleading remarks.
The comparison of error handling was especially egregious; the code example for that was nonsense.
The "Chain" sub-section was really about transforming values. It also failed to demonstrate chaining promise `.then`s.
Reworked these sub-sections and improved the code samples to match.
PR Close#51516
Previously, the `retry` example did not work as intended. The `retry`
operator was called before the exception occured, thus not retrying the
`ajax` request.
This commit moves the `retry` operator into the correct order to ensure
that the failed request is retried.
PR Close#38905
