update interface vs type aliases docs, to include features supported …

[cryptoB0T]

…since ts 2.7

Fixes #
The docs should indicate that type aliases can be extended, as this is supported since 2.7.

[orta]

I tried looking through the release notes but I couldn't find anything about this feature, do you mean something like this?

type MyType = {
  a: boolean
}

type MyExtendedType = MyType & { b: string }

declare const extended: MyExtendedType

extended.a
extended.b

[cryptoB0T]

yes, this is correct. the docs appear to indicate that type aliases cannot be extended. it doesn't appear in the release notes but the TS compiler seems to support this functionality. is there something I'm missing?

[orta]

Yeah, I also was a little stumped - but that's fine, I've tried to update the PR to include that info with an example to make it more concrete 👍

[orta]

Thanks!