Not true. I've seen some very successful large webapps in poorly-written Java.

node.js is written in JavaScript.

I am aware of that, but I personally use JavaScript to mean the browser language, and all the browser's features (DOM, WebSocket, etc.), but node.js to mean JS in the node.js environment. Same core language, but different environments, so not the same in practise.

Large parts are written in C++ :)

I'm pretty sure that very little of it is actually in js. It's more appropriate to say that you use javascript to script the node environment/runtime.

Actually a pretty decent part is in JS since most of the standard libraries are purely written in JS. Github claims that nearly 70% of the node repository is in JavaScript.