In some third-party code I found a strange type definition which I didn't see before.

type SomeType = [from: number, to: number];

No idea how this is called in docs so I could not find anything about it. Can someone explain me please what does it mean?

PS. const q: SomeType = [1, 2]; compiles just fine so I guess it's still a simple array of two numbers.

CodePudding user response：

It is Labeled tuple elements

Treat labels from and to just as a comments. They don't affect type itself in any way. It is just for readability.