node.js doesn't just resemble JavaScript, it is JavaScript. Like ES5 standard JavaScript, and (very soon) ES6 standard JS as well. It uses the V8 JS engine.
The only non-standard features of Node.js has been the module system (CommonJS), but even that will be ECMA standard as of next version.
Agreed. I use ES6 modules regularly (via Babel compiled to CommonJS, and also Rollup). Unlike CommonJS, ES6 modules have the advantage (and disadvantage) of being statically resolved, which permits tree-shaking (but denies dynamic resolution of imports like CommonJS).
The "that" in my sentence refers to "module system", not "CommonJS", but I agree my sentence was unclear.
The only non-standard features of Node.js has been the module system (CommonJS), but even that will be ECMA standard as of next version.
(also, Node.js was built in C++ and JS)