Notable a lot of JavaScript AST libraries at least a while back omitted comments and whitespace, which is fine for writing a minifier, but horrible when trying to implement source code transformations.
What I really like about Roslyn's AST (and I guess TypeScript's looks about the same) is that all those details are put into Trivia; ignoring those is just passing one flag to the visitor; you don't have to be aware of how many different types of AST nodes there are that might be ignorable. It also means that each and every whitespace and comment belongs to a syntax token instead of being other nodes interleaved with the normal nodes. This helps keeping comments where they belong even after re-arranging code in the AST – something that, e.g. ReSharper is atrociously bad at.
What I really like about Roslyn's AST (and I guess TypeScript's looks about the same) is that all those details are put into Trivia; ignoring those is just passing one flag to the visitor; you don't have to be aware of how many different types of AST nodes there are that might be ignorable. It also means that each and every whitespace and comment belongs to a syntax token instead of being other nodes interleaved with the normal nodes. This helps keeping comments where they belong even after re-arranging code in the AST – something that, e.g. ReSharper is atrociously bad at.