It's pretty clear that JavaScript is better than C. It's even pretty clear that it's better than PHP.
It's debatable (and I would certainly debate it, in some cases) as to whether JavaScript is better than your-favorite-high-level-language, but it seems clear that JavaScript is "good enough" for server-side work.
This isn't so much a reason as a pre-emption of an argument, that JS is somehow a "toy". It's hard to reasonably make the argument that that is so: billions of dollars have been invested in improving its performance, its reliability, and those investments have been directly leveraged by Node in the form of V8.