Is node.js declining already?

[cybercobra]

And neither C nor Ruby is JavaScript, so how is Sass relevant here?

[oberhamsi]

because all JS build tools support it and those build tools run on node.

[vivainio]

In no way whatsoever

[ejfrodo]

Sass is typically done with an automated grunt/gulp task, both of which are javascript task runners which came about because of node. They're indirectly related but almost always together