Quantum computing has nothing to do with what what we would consider "regular" computing. Even if it became practical, at most it would be a specialized accelerator for certain types of computation, like factoring numbers.
Quantum computing is still in the "researchers are playing with a handful of Qbits" stage, approximately where transistors where a hundred years ago. Scaling quantum computers is really hard. Even though Qbits can be encoded in single atoms, the machinery that keeps the quantum states stable and manipulates them is most definitely not easy to shrink.
It's also completely unclear whether quantum computers would make your Javascript engine run any faster.
My understanding is Quantum computing isn't the next generation of computing, it's more of a new type of computing. It's an improvement on a certain class of problems (such as optimization algorithms).
I believe the point of this article was to discuss the possibilities outside of, and up until, that realm.