That's because they are. Functional code is more readable. And if you look back, basically all advances in programming languages have been about "making stuff more readable". Thus, for loops (for this usage) are "old".
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.
Readability is a characteristic of the reader, not what is being read.
This simple truth seems to be so hard for many people to internalize. My theory as to why is that most programmers never get exposed to drastically different and unfamiliar languages and styles of programming. If they were forced to confront and internalize 2-3 different ways of writing code, they would realize this truth.
Personally, I once thought Lisp was unreadable... until I learned it. I once thought BASH was unreadable... until I learned it. Same with half a dozen other languages. Same for styles. "Readability" is just a familiarity and proficiency of the reader.
There is no way that
is more readable than