Generating random whole numbers in JavaScript in a specific range?

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How can I generate random whole
numbers between two specified variables in JavaScript, e.g. x =
4 and y = 8 would output any of 4, 5,
6, 7, 8?

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class="normal">Answer

There are
some examples on the href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Math/random"
rel="noreferrer">Mozilla Developer Network
page:

/**
 * Returns a
            random number between min (inclusive) and max (exclusive)

            */
function getRandomArbitrary(min, max) {

 return
            Math.random() * (max - min) + min;
}

/**
 *
            Returns a random integer between min (inclusive) and max (inclusive).
 * The
            value is no lower than min (or the next integer greater than min
 * if min
            isn't an integer) and no greater than max (or the next integer
 * lower than
            max if max isn't an integer).
 * Using Math.round() will give you a
            non-uniform distribution!
 */

function getRandomInt(min,
            max) {
 min = Math.ceil(min);
 max = Math.floor(max);

            return Math.floor(Math.random() * (max - min + 1)) +
            min;
}

/>

Here's the logic behind it. It's a simple rule of
three:

Math.random()
returns a Number between 0 (inclusive) and 1 (exclusive). So we
have an interval like this:

[0
            ....................................
            1)

Now, we'd like a
number between min (inclusive) and max
(exclusive):

[0
            .................................... 1)
[min
            ..................................
            max)

We can
use the Math.random to get the correspondent in the [min, max)
interval. But, first we should factor a little bit the problem by subtracting
min from the second
interval:

[0
            .................................... 1)
[min - min
            ............................ max -
            min)

This
gives:

[0
            .................................... 1)
[0
            .................................... max -
            min)

We may now apply
Math.random and then calculate the correspondent. Let's choose
a random number:

            Math.random()
 |
[0 ....................................
            1)
[0 .................................... max - min)


            |
 x (what we
            need)

So, in order to
find x, we would
do:

x = Math.random() * (max -
            min);

Don't forget to
add min back, so that we get a number in the [min, max)
interval:

x =
            Math.random() * (max - min) +
            min;

That was the
first function from MDN. The second one, returns an integer between
min and max, both
inclusive.

Now for getting integers, you could
use round, ceil or
floor.

You could use
Math.round(Math.random() * (max - min)) + min, this however
gives a non-even distribution. Both, min and
max only have approximately half the chance to
roll:

min...min+0.5...min+1...min+1.5
            ... max-0.5....max
└───┬───┘└────────┬───────┘└───── ... ─────┘└───┬──┘ ←
            Math.round()
 min min+1
            max

With
max excluded from the interval, it has an even less chance to
roll than min.

With
Math.floor(Math.random() * (max - min +1)) + min you have a
perfectly even
distribution.

min.... min+1...
            min+2 ... max-1... max.... max+1 (is excluded from interval)

| | |
            | | |
└───┬───┘└───┬───┘└─── ... ┘└───┬───┘└───┬───┘ ← Math.floor()

            min min+1 max-1
            max

You can't use
ceil() and -1 in that equation because
max now had a slightly less chance to roll, but you can roll
the (unwanted) min-1 result too.