Earlier quoted context omitted.
I'm not even sure there's an implementation that could do even the most common synchronous operation. Like opening a socket, sending data, and blocking on the response.
I'm not sure if you mean implementation of JS or of something that supports executing JS. If you start with the bare interpreter and add say, global functions, through the interpreter's extension API, they CAN be synchronous. You COULD produce a JS environment this way and run scripts in it. Your extensions could include synchronous usage of sockets. Your programs in this environment would be synchronous. Writing a d…
You can find some of it, but it's the exception, not the rule.
Yes, you can build something specific, just as you can leverage async libraries in languages where it's not the common pattern.