如何在Javascript中的两个指定变量之间生成随机整数，例如x = 4和y = 8会输出4,5,6,7,8中的任意一个？

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There are some examples on the 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)
 * Using Math.round() will give you a non-uniform distribution!
 */
function getRandomInt(min, max) {
    return Math.floor(Math.random() * (max - min + 1)) + min;
}

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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.

---

var randomnumber = Math.floor(Math.random() * (maximum - minimum + 1)) + minimum;

---

Math.random()

From the Mozilla Developer Network documentation:

// Returns a random integer between min and max

function getRandomInt(min, max) {
  return Math.floor(Math.random() * (max - min + 1)) + min;
}

Useful examples:

// 0 - 10
Math.floor(Math.random() * 11);

// 1 - 10
Math.floor(Math.random() * 10) + 1;

// 5 - 20
Math.floor(Math.random() * 16) + 5;

// -10 - (-2)
Math.floor(Math.random() * 9) - 10;

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