Subscribe Arguments

You might have seen that we deprecated some signatures of the subscribe method, which might have caused some confusion. The subscribe method itself is not deprecated. This deprecation also affects the tap operator, as tap supports the same signature as the subscribe method.

This is to get ready for a future where we may allow configuration of subscribe via the second argument, for things like AbortSignal or the like (imagine source$.subscribe(fn, { signal }), etc). This deprecation is also because 2-3 function arguments can contribute to harder-to-read code. For example someone could name functions poorly and confuse the next reader: source$.subscribe(doSomething, doSomethingElse, lol) With that signature, you have to know unapparent details about subscribe, where using a partial observer solves that neatly: source$.subscribe({ next: doSomething, error: doSomethingElse, complete: lol }).

In short we deprecated all signatures where you specified an anonymous error or complete callback and passed an empty function to one of the callbacks before.

What Signature is affected

We have deprecated all signatures of subscribe that take more than 1 argument.

We deprecated signatures for just passing the complete callback.

import { of } from 'rxjs';

// deprecated
of([1,2,3]).subscribe(null, null, console.info); // difficult to read
// suggested change
of([1,2,3]).subscribe({complete: console.info});

Similarly, we also deprecated signatures for solely passing the error callback.

import { throwError } from 'rxjs';

// deprecated 
throwError('I am an error').subscribe(null, console.error);
// suggested change
throwError('I am an error').subscribe({error: console.error});

Do notice, in general it is recommended only to use the anonymous function if you only specify the next callback otherwise we recommend to pass an Observer

import { of } from 'rxjs';

// recommended 
of([1,2,3]).subscribe((v) => console.info(v));
// also recommended
of([1,2,3]).subscribe({
    next: (v) => console.log(v),
    error: (e) => console.error(e),
    complete: () => console.info('complete') 
})