Apparently Math.random() in V8 only works with 32 bit values (and didn't even correctly randomize all of those in the past). And with 32 bits, the probability of a collision reaches 50% around 2^16 = 65k values...
32bits of randomness seems like plenty for most applications, and if you need more than that you should really specify that explicitly. If it speeds up Math.Random() for 90% of uses that seems like a reasonable optimization to me.
FWIW, it wasn't enough randomness for me. I was seeing collisions in some trivial code in Chrome that worked fine in every single other browser. It's not like Chrome's Math.random performance is significantly better than other modern browsers.
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[ 2.8 ms ] story [ 18.8 ms ] threadApparently Math.random() in V8 only works with 32 bit values (and didn't even correctly randomize all of those in the past). And with 32 bits, the probability of a collision reaches 50% around 2^16 = 65k values...
Here is bug report: https://code.google.com/p/chromium/issues/detail?id=276886