HTML doesn't do anything for JS other than provide a way to create visual interfaces. It might be comparable to the role that `tkinter` plays for Python's stdlib, but HTML alone is emphatically not a standard library.
My point is that most languages are totally useless on their own. JavaScript the _language_ doesn't offer any FFI or other mechanism to call outside services. Without a browser or something like Node's libuv, JavaScript wouldn't be useful at all. The capabilities provided in the box are part of the language in terms of what actually matters in motivating people to choose to use the language, no matter what form those capabilities come in.