To me, it's the event-driven problems JS tries to solve that seems to overlap with typical server functionality. That has been true since the beginning.
What, that you clicked a button and JS did something back in 95 when Netscape introduced it? The same could be said for Visual Basic for any language that had callback code attached to a button click. You do realize that Python, Perl, etc could be written to handle GUI code back then as well.
JS has been focused on event handling types of problems while python and perl were used for many other types of problems. You can build a GUI with R, but it wasn't made for it.
