According to some recent research[2], the three primary factors affecting the adoption of a programming language by developers are, in this order:
1. Libraries available
2. Familiarity
3. Performance
And per the paper, this order of preference is extremely strong. Which means, because of the huge mass of Javascript developers out there, that as soon as a library becomes available to do something in Javascript, Javascript will rapidly become the most popular way to do that thing, regardless of the performance hit.
[1] http://redmonk.com/sogrady/2012/09/12/language-rankings-9-12... [2] http://www.eecs.berkeley.edu/~lmeyerov/projects/socioplt/pap...