Outside Google, ClojureScript (with a "j") used to depend on the Closure compiler (with an "s") - partly because the library that came with the compiler provided a Java-like API which was convenient as the Clojure language was originally written targeting Java, and partly because the language had quite a large runtime and tree shaking was necessary for performance. You also had to write extern declarations if you used outside code, much like you have to manually declare types for untyped dependencies in when using Typescript.

Edit: ClojureScript still depends on Google Closure.