If you really wanted to determine 'most important', think about what software you'd be left with if all software and dependencies written in a language was taken away.
Take away JS and a bunch of webapps don't run. Take away C and you have no OS, no web servers, no languages whose leading implementations don't bootstrap themselves, no TomToms telling you how to get to JSconf, and so on.
I do understand the renewed hype behind Javascript, but to enshrine it as most important -- talk about hyperbole and a lack of perspective.
PS: That V8 engine you'd be relying on for your JS -- it's not written in Javascript either.