Javascript random number generator in range, going below and above the given range

Question

I have been trying to make a random number generator, with a given range, thought it would be easy and then without any logical reason the random number isnt in any way affected by the given maximum and minimum range. Please help. Here is the code:

<!DOCTYPE html>
          <html>
           <head>
             <style>
                .elements {
                text-align: center;
                 }

           .random {
                margin-top: 100px;
                width: 275px;
                height: 200px;
                font-size: 50px;
                text-align: center;
            }

            .range {
                margin: 35px 25px;
                width: 100px;
                height: 100px;
                text-align: center;
                font-size: 30px;
            }

            .generate {
                margin-top: 50px;
                width: 250px;
                height: 35px;
                font-size: 20px;
            }
        </style>

        <script language="javascript" type="text/javascript">
            function rand()
            {
                var max = document.getElementById("max").value;
                var min = document.getElementById("min").value;

                var output = document.getElementById("output");

                var random = Math.floor(Math.random() * max + min);

                output.value = random;
            }
        </script>

    </head>
    <body>
        <div class="elements">

        <input type="text" class="random" id="output">
        <br>
        <input type="button" class="generate" value="Generate random number" onclick="rand();">
        <br>
        <h1>Maximum Number</h1>
        <input type="text" class="range" id="max">
        <h1>Minimal Number</h1>
        <input type="text" class="range" id="min">

        </div>
    </body>
</html>

Math.floor(Math.random() * max + min); This causes that Math.random() is multiplicated with max and after that, min is added via the plus. — Tyr
– Tyr, Commented Apr 27, 2018 at 17:59

CertainPerformance · Accepted Answer · 2018-04-27 18:10:28Z

3

You need to multiply Math.random() by the length of your range, not by the maximum value in the range.

const getRandom = (min, max) => Math.floor(Math.random() * (max - min + 1) + min);
Array.from({ length: 20 }, () => console.log(getRandom(0, 2)));

answered Apr 27, 2018 at 18:10

CertainPerformance

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Comments

set0gut1 · Accepted Answer · 2018-04-27 18:18:05Z

1

document.getElementById("max").value is string, so now Math.random() * max + min is float * string + string, which append min value as string. parseInt will resolve this issue.
Math.random() * max + min is incorrect. Math.random() * (max - min + 1) + min is right.

edited Apr 27, 2018 at 18:18

answered Apr 27, 2018 at 18:10

set0gut1

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2 Comments

set0gut1 Over a year ago

But in my browser, 0.01 * "10" + "999" is 0.1999.

Scott Sauyet Over a year ago

Yes, multiplication coerces the string to a number, but addition does not.

Philip · Accepted Answer · 2018-04-27 18:27:35Z

Add a code block that checks if the random number generated falls in the range specified. If it doesn't loop through random number generation until the condition test fails;

function rand() {
  var max = document.getElementById("max").value;
  var min = document.getElementById("min").value;

  var output = document.getElementById("output");


  var random = Math.floor(Math.random() * max + min);

  while (random > max || random < min) {
    random = Math.floor(Math.random() * max + min);
  }

  output.value = random;

}

.elements {
  text-align: center;
}

.random {
  margin-top: 100px;
  width: 275px;
  height: 200px;
  font-size: 50px;
  text-align: center;
}

.range {
  margin: 35px 25px;
  width: 100px;
  height: 100px;
  text-align: center;
  font-size: 30px;
}

.generate {
  margin-top: 50px;
  width: 250px;
  height: 35px;
  font-size: 20px;
}

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<div class="elements">
  <input type="text" class="random" id="output">
  <br>
  <input type="button" class="generate" value="Generate random number" onclick="rand();">
  <br>
  <h1>Maximum Number</h1>
  <input type="text" class="range" id="max">
  <h1>Minimal Number</h1>
  <input type="text" class="range" id="min">

after that, you can then assign the its value to output.

Tuychiev Toir · Accepted Answer · 2019-03-11 08:59:26Z

0

using this code:

// the initial seed
Math.seed = 6;

// in order to work 'Math.seed' must NOT be undefined,
// so in any case, you HAVE to provide a Math.seed
Math.seededRandom = function(max, min) {
    max = max || 1;
    min = min || 0;

    Math.seed = (Math.seed * 9301 + 49297) % 233280;
    return Math.floor(min + (Math.seed / 233280) * (max - min));
}
var res = Math.seededRandom(100,-100)
console.log(res)

or try it yourself

http://indiegamr.com/generate-repeatable-random-numbers-in-js/

edited Mar 11, 2019 at 8:59

answered Mar 11, 2019 at 8:51

Tuychiev Toir

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