Deprecations in RxJS v6.4.0
I’ve been trying to cover some of the things that came along this new version of RxJS. So, after writing about a tiny new feature and a bugfix, now is time to look at the deprecations.
Deprecate null parameter signatures for subscribe
(PR that introduced the deprecation)
Do you often find yourself using null (or undefined) instead of callback functions when subscribing to an Observable? Do you find that annoying? Well, starting from this release, that practice is now discouraged. The recommended way is to use an “observer”.
What is an “observer” you might be asking? It’s an object that has three properties — next, error and complete. Each property is used for the corresponding callback function.
With that in mind, here’s a list of all deprecated signatures and their recommended alternative (StackBlitz):
import { of } from 'rxjs';
const source = of(3, 2, 1);
// Deprecated
source.subscribe(
null,
null,
() => console.log('Complete. Cookie time.')
);
// Recommended
source.subscribe({
complete: () => console.log('Complete. Cookie time.')
});
// ---
// Deprecated
source.subscribe(
null,
error => console.error(error),
() => console.log('Complete. Cookie time.')
);
// Recommended
source.subscribe({
error: error => console.error(error),
complete: () => console.log('Complete. Cookie time.')
});
// ---
// Deprecated
source.subscribe(
value => console.log(value),
null,
() => console.log('Complete. Cookie time.')
);
// Recommended
source.subscribe({
next: value => console.log(value),
complete: () => console.log('Complete. Cookie time.')
});
One thing you might have noticed is that by using the “observer” object, you can specify only the callbacks you’re interested in. Yes, it’s true. And it’s quite flexible. No more null (undefined)!
Deprecate null parameter signatures for tap
(PR that introduced the deprecation)
Did you know that tap can take next, error and complete callbacks? Honestly, I didn’t. I always thought tap takes only one function. So seeing this deprecation surprised me a bit but in a positive way because I discovered something new.
Anyway, since tap takes the same type of callbacks as subscribe, that means the deprecation is the same as well.
Because of that, I’m not going to repeat the same examples from above. Instead, I’m going to show you just one. You can figure out the rest yourself (StackBlitz):
import { of } from 'rxjs';
import { tap } from 'rxjs/operators';
const source = of(3, 2, 1);
source.pipe(
// Deprecated
tap(null, null, () => console.log('Complete. Cookie time.'))
).subscribe(...);
source.pipe(
// Recommended
tap({
complete: () => console.log('Complete. Cookie time.')
})
).subscribe(...);
Deprecate create method
(PR that introduced the deprecation)
Are you using the create method to create new Observables/Subjects? The recommended way now is to use the new keyword (StackBlitz):
// Deprecated
const o = Observable.create(...);
const s = Subject.create();
// Recommended
const o = new Observable(...);
const s = new Subject();
So there it is. Things to keep in mind (and avoid) when working with RxJS.
Hope you learned something new today. I certainly did.
Until next time :)