Nothing in that snippet is Typescript-specific, it's just plain Javascript.
All syntactically valid Javascript is also syntactically valid Typescript, it just adds stuff, though you can get runtime errors for things like reassigning variables in a way Javascript is fine with that Typescript disallows.
All syntactically valid Javascript is also syntactically valid Typescript, it just adds stuff, though you can get runtime errors for things like reassigning variables in a way Javascript is fine with that Typescript disallows.