This is not only about extra computational performance, but also about predictability, I'd love to program on a hard real time system with Go instead of C++, but given it uses GC, it is not going to happen. I have mostly worked on real time embedded systems, and I only encountered C and C++, mostly because there is no other sane choice available.
If the fashionable choice is to use C++ for example, a lot more can go wrong if the programmer isn't doing thing right.
Now if you have the same situation with a higher level language, the worst that can happen is infinite loops.
Most projects don't need the extra performance C++ would provide. So most of the time it's a better choice to use a higher level, more predictable language like Node.js or Go.
Since ECMAScript engines like V8 have been optimised a lot in the last years too, the performance difference is not that high either.