fix(startWith): fix incorrect types

[jorroll]

Description:

I think (not sure) that the function definition of startWith is incorrectly typed. Because startWith has function overloads, this incorrect typing has no direct user impact. Except! this incorrect function signature is shown in the documentation for startWith (at the top), creating a source of confusion: https://rxjs-dev.firebaseapp.com/api/operators/startWith

This change can be thought of as a documentation fix, though it is also updates (fixes) the internal typing of the startWith operator function.

Related issue (if exists):

[cartant]

Nope. IMO, it is correctly typed. The D refers to the type of the argument passed to the operator and the T refers to the type of the value received from the source.

[jorroll]

@cartant what you said sounds correct, but I don't think that startWith currently has that function signature... ?

Currently startWith looks like:

startWith<T, D>(...array: Array<T | SchedulerLike>)

But shouldn't it look like?

startWith<T, D>(...array: Array<D | SchedulerLike>)

After all,

D refers to the type of the argument passed to the operator

[jorroll]

As a point of comparison, the type signature of the startWith function itself appears to be incompatible with its second function overload.

i.e. this is the first function overload:

function startWith<T, D>(v1: D, scheduler: SchedulerLike): OperatorFunction<T, T | D>;

and this is the type signature of the function:

function startWith<T, D>(...array: Array<T | SchedulerLike>): OperatorFunction<T, T | D>

[cartant]

Yeah. You're right. I read the diff backwards.