Random Number generator

Math.random() gives a number from and including 0 to and not including 1. This means that the following code gives a random number from 0-5

var randomNumberBetween0And5 = Math.floor(Math.random() * 6)

This is because Math.random() * 6 can vary from 0 (Math.random() = 0) to 5.999 (Math.random() = 0.9999), and when rounding down using Math.floor this becomes 0-5.

We would now like a lower bound, so let's say we want the numbers from 1-6 instead, we could then do the following:

var randomNumberBetween1And6 = Math.floor(Math.random() * 6) + 1

In this case 1 is the lower bound, but this works for any lower bound.

Now I will explain this:

(upper - lower + 1 )

We can see why this is the case by looking at our example above, where we want the numbers from 1-6. This means that upper=6 and lower=1, which means that upper-lower=5, i.e, the random value would be between 1-5, which means that 6 is not included. Therefore we add 1, such that we include the upper value, which in this case was 6.