function rnd(j){
arr = [0,0]
for(i=0;i<=j;i++){
r = Math.round(Math.random())
arr[r] = arr[r]+1
}
a = arr[0] / arr[1] * 100
return a
}

This function tests how random will the Math.random() function be. You can test it with rnd(1000000) a couple of times to get results.

Test randomness in JavaScript

JavaScript