According to this post on the official V8 Javascript blog, the pseudo-random number generator (PRNG ... looking at a plot of some values. The code that generated the images is here.

Of course, it is easy to create a very long pseudorandom sequence in software, but even the best PRNG (Pseudorandom Number Generator) needs a good random seed, as we don’t want to get the same ...

Quantum physics plays by a different set of rules, one with its own built-in random number generator determining a particle's properties. As far as we know, there are no hidden strings at work ...