RxJS 7 is released 🎉
Tags: webdev, functional, javascript
Published: 2021-05-06 19:21:17

# Intro

RxJS v7.0.0 was released just a few days ago, after a more-than-one-year long beta period. It is definitely the most used reactive extension library used for JavaScript with ~24 millions download per week.
[Npm page](https://www.npmjs.com/package/rxjs)

There are no removal yet, but a lot of deprecations - that will be removed later - so it is recommended to allocate time for the RxJS update! 

## What's new
It is not that much upgrade that was the previous major package updates, but there are several notable differences between version 6 and seven, let's take a closer look.

#### Smaller bundle size

It is worth a point that the whole package had been walked through by the creators to check out where are possibilities to - at the end - reduce the bundle size. There were no major refactor with the app - as I saw and read.

![image](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/mi59kjrqrru77jvegg97.png)
 
Maybe the reduce size is not that outstanding, but every kB counts with slow network especially on mobile. You may see the reducing trend in the chart, it is a good way to go. :)

You can check out the bundle size here, on [Bundlephobia](https://bundlephobia.com/result?p=rxjs@7.0.0).

#### Latest TypeScript & better type interference

RxJS uses the latest TypeScript (as of 2021.05.06) and also has some real improvements interfering different types. The limit, that around ~7/8 argument RxJS was not able to handle types no longer exists!

There is another example for this, let's take a look at this.
```
of(new Date(), null, undefined)
  .pipe(filter(Boolean))
  .subscribe();
```
Now, the type will be `Observable<Date>`, but it was `Observable<undefined>` in RxJS 6.

#### toPromise deprecation

Maybe this is not relevant for someone but a lot of projects may be affected from this. `toPromise` is deprecated in RxJS 7 and there are two new operators replacing this one, called `firstValueFrom` and `lastValueFrom`. It is a huge improvement for reliability for many codebases.

AS the name indicates, `firstValueFrom` resolves with the first value of a stream, and `lastValueFrom` return with the last value from the observable stream. **If no values emitted, an error is thrown.** Unlike toPromise, which resolves simply with undefined.

#### Operators renamed

I remember we had a discussion with the team that: "wish the operators in RxJS could have more talkative names". It happened, so the following operators are renamed

* combineLatest -> combineLatestWith
* merge -> mergeWith
* zip -> zipWith
* concat -> concatWith
* race -> raceWith

#### Retry operator with resetOnSuccess

Previously the retry operator's parameter was not reseted after successful attempts. Now there is a configuration option to indicate this.

```
...
retry({ count: 2, resetOnSuccess: true })
...
```
#### Removing multiple callback options

In RxJS 7 the multiple callback for done, error, complete had been removed from `tap` and `subscribe`. Now you need to pass an object for these configuration, just to force you to think it two times and make sure.

Now, instead of this
```
obs$.pipe(tap(
  data => console.log(data),
  error => console.log(error)
)).subscribe(
  data => console.log(data),
  error => console.log(error)
)
```

Now you have to do the following:
```
source$.pipe(tap(
  data => console.log(data)
)).subscribe(
  {
    next:  data => console.log(data), 
    error:  err => console.log(err),
  }
)
```

#### Faster

According to some tweets and discussions, developers claims that RxJS 7 is faster. Still, it needs to stand the probe of time, but I think it will. :)


##### Footnote

Of course there are several other updates in RxJS and shoutout to the developer team for releasing this package. You can read more about the update in details on the following links:

[Change summary](https://github.com/ReactiveX/rxjs/blob/master/docs_app/content/6-to-7-change-summary.md)
[Medium article](https://medium.com/volosoft/whats-new-in-rxjs-7-a11cc564c6c0)
[inDepth article](https://indepth.dev/posts/1353/the-state-of-rxjs-rxjs-7-and-beyond)