Proposal: IfAny, IsAny, IsUnknown, etc

[sindresorhus]

https://github.com/sindresorhus/type-fest/pull/127/files#r474306457

Thoughts?

[Milo123459]

@sindresorhus I think this would be very helpful.

[sindresorhus]

What would you use it for?

[Milo123459]

I have a new package I'm working on, which works with objects. This would help me manage things.

If this doesn't get added, I don't really mind, it's already an amazing library. Thanks @sindresorhus 👍

[sindresorhus]

Alright. This is PR welcome.

The submitter should make sure to follow https://github.com/sindresorhus/type-fest/blob/master/.github/contributing.md closely.

[sindresorhus]

If anyone wants to work on this, see the initial attempt in #505

Instead of IfAny, we could potentially do what's done in #544 Feedback wanted on that way of handling it.

[tommy-mitchell]

I've started working on this, but I'm struggling to think of use cases for these beyond being helpers in other types.

I also started by making both an IsAny and an IfAny in is-if-any.d.ts (etc.), but I found that unional/type-plus#201 combined them like so:¹

type IsAny<T, TypeIfAny = true, TypeIfNotAny = false> = 0 extends 1 & T ? TypeIfAny : TypeIfNotAny;

IsAny<any> //=> true
IsAny<number> //=> false
IsAny<any, number, string> //=> number

I kind of like that IsAny and IfAny are more explicit in what they do, but the succinctness of this method is nice. Thoughts?

Footnotes

1. Really, it was IsNever, but it's the same difference. ↩