Y.Alea is a better pseudorandom number generator than Math.random.

based on Alea.js and Mash.js.
Copyright (C) 2010 by Johannes Baagøe <baagoe@baagoe.org>

http://baagoe.org/en/w/index.php/Better_random_numbers_for_javascript

Better Than Math.random!

To summarize Johannes Baagøe's arguments

Math.random may be implemented differently in different environments. This makes it impossible to control the quality of the pseudorandom numbers in your application.
Math.random does not allow custom seed values. Random sequences can not be easily repeated for testing or other purposes.
Math.random is not cryptographically secure.

Y.Alea is based on the Alea pseudorandom number generator which aims to solve these problems.

Using Y.Alea

Y.Alea is a constructor that will accept any number of arguments. Together, these arguments form the seed value. If no arguments are given, the current time will be used as the seed value. Instances of Y.Alea have three methods for generating random numbers:

random: The random method is intended to be used in place of Math.random. It will return a number that is greater than or equal to 0 and less than 1. The random method is also the core implementation of Alea; the other methods derive from it.
fract53: The fract53 method works just like the random method except it will return floating point values of greater precision. The extra precision comes with a small performance cost.
uint32: The uint32 method returns integers instead of floating point values. It will return a number greater than or equal to 0 and less than 4294967296.