Even with a case of Red Bull, a bottle of Adderall, and a heart full of courage, I doubt most of us could come close to that level of productivity. We'd get bogged down in the details. I know I would.
More over there was no social media sites like twitter, facebook, etc, at that time :)
But arguably (Doug Crockford may have argued this) the whole process required JS to make more out of fewer, stronger primitives (first-class functions, prototypes). I know I didn't have time for much else, as I said at the ICFP 2005 keynote.
As I told Peter Seibel in "Coders at Work", besides lack of time, I couldn't add anything like (Pythonic, dynamic) classes. That would have encroached on Batman-Java; can't have JS-Robin-the-boy-hostage getting too big for the Netscape/Sun-1995-era-batcave.
An analogous situation is your average first year PhD candidate. Initially making some sort of contribution to the field feels overwhelming and almost impossible. But once you've spend a year or two reading papers and having coffee with the leaders in the field, everything comes together. That same PhD student starts to churn out quality papers every 6 months or so.
I think back to what it was like watching my dad program in Scheme when I was in high school. I got the same curious and overwhelming feeling then as I do now when working on certain areas of distributed systems. There's no reason to believe that the barriers that grownups face are any less insurmountable than the ones children do. :)