Since JS is the only thing you can actually use[1] in a browser you can argue that anything that runs in the browser is syntactic sugar (and in fact, Typescript is syntactic sugar).

A less flippant analogy might be macro support in Rust. It's clearly part of Rust, but the syntax is completely different and it requires IDEs to have completely separate processing just to handle it. I wouldn't consider that to be mere syntactic sugar either.

[1] Yes, yes, wasm