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From: Lasse Reichstein Nielsen on 1 May 2010 15:30
VK <schools_ring(a)yahoo.com> writes:

> Assuming one needs to have a function returning false or true on each
> call in pseudo-random order.and using JavaScript native Math.random()
> method as the basis of the pseudo-randomness. Say the variants of such
> function are:
>
> getAnswer1() {
> var n = Math.round(Math.random());
> return n ? true : false;
> }
>
> getAnswer2() {
> var n = Math.floor(Math.random()*2);
> return (n==2) ? true : false;

As stated elsewhere, this should read
return (n == 1) ? true : false;
or, preferably,
return n == 1;

> }
>
> Leaving obvious practical testing by platforms aside:
>
> Is there are theoretical considerations that pseudo-randomness
> (predictability) of either of above will be better or worse than the
> other one?

No, they are (obviously?) exactly identical. They map exactly the same
results of Math.random() to true and false respectively.
In both cases, a value in the range [0..0.5[ is mapped to false
and a value in the range [0.5..1[ is mapped to true.

> JavaScript Kit site claims that the second bits first:
> http://www.javascriptkit.com/javatutors/randomnum.shtml
> but they don't disclose the underlaying reasoning.

I guess their point is that to generate an integer in the range [0..n[,
Math.floor(Math.random() * n)
is better, in general, than
Math.round(Math.random() * (n - 1))
.... which is pretty old news (not that people still don't bungle it
regularly, but it's embarrasing every time it happens).

The funny thing is that for n = 2, the unevenness of using the Math.round
doesn't matter, which is the case you are asking about.

--
Lasse Reichstein Holst Nielsen
'Javascript frameworks is a disruptive technology'

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