Instead of providing a seed, which will be used to seed our Mersenne Twister, you can also specify an arbitrary function to generate random numbers which the rest of the library will utilize when generating everything else.
A rather simple example, simply using Math.random() instead of our Mersenne Twister
// Use Math.random() instead of our Mersenne Twister
var chance = new Chance(Math.random);
chance.address()
=> '131 Asmun Pike'
chance.address()
=> '261 Pawnaf Highway'
Chance will appear to work just the same, but have a different underlying random generator.
This function should return any number between 0 and 1.