startWith Deprecation warning

I can’t find any documentation on what is actually deprecated, but I believe this is related to: https://github.com/ReactiveX/rxjs/issues/4723.

Bug Report

Current Behavior startWith is deprecated: use {@link scheduled} and {@link concatAll} (e.g. scheduled([[a, b, c], source], schedul er).pipe(concatAll()))

Reproduction

startWith(null);

Expected behavior No deprecation warning

Environment

• RxJS version: 6.5.2

[orjandesmet]

The deprecation warning also disappears when typing the null in startWith. By default it’s typed any, so I guess the compiler doesn’t know it’s not meant to be a SchedulerLike.

startWith(<string>null); // In case your stream emits strings

[cartant]

The problem is related to the issue you referenced only in that some operators and observable creators that have signatures that include a Scheduler parameter have those signatures deprecated.

In your case, startWith(null) is matching this signature:

export function startWith<T>(scheduler: SchedulerLike): MonoTypeOperatorFunction<T>;

And it only matches that signature because you most likely have "strictNullChecks": false in your TypeScript configuration - either explicitly or implicitly.

Given that this is not a problem for in situations in which strictNullChecks are enabled, IMO, the deprecation should be left in place and a TSLint flag should be used to suppress the warning:

// tslint:disable-next-line:deprecation
startWith(null)