Suggestion: More narrow type for Math.sign

[kreba]

The type for Math.sign is currently (x: number): number as seen in
https://github.com/Microsoft/TypeScript/blob/master/lib/lib.es6.d.ts#L4177

Its type could be (x: number): -1 | 0 | 1 instead.

That would allow for more specific typing in app code without having to wrap Math.sign.

[aluanhaddad]

This would be great but

Math.sign(NaN) // NaN
typeof NaN // "number"

which poisons what would otherwise be quite elegant behavior.

[mhegazy]

discussed previously in #15356

[kreba]

Thank you for your immediate response!

I had never considered what happens with NaN. Now I understand why it's return type is currently number.

I'll continue wrapping it for my comparators then.