Generate random number between two numbers in JavaScript

Question

Is there a way to generate a random number in a specified range  e g  from 1 to 6  1  2  3  4  5  or 6  in JavaScript

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This is about nine years late  but randojs com makes this a simple one-liner   rando 1  6    You just need to add this to the head of your html document  and you can do pretty much whatever you want with randomness easily  Random values from arrays  random jquery elements  random properties from objects  and even preventing repetitions if needed    lt script src  https   randojs com 1 0 0 js  gt  lt  script gt

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to return 1-6 like a dice basically   return Math round Math random     5   1

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Math is not my strong point  but I ve been working on a project where I needed to generate a lot of random numbers between both positive and negative     function randomBetween min  max        if  min  lt  0            return min   Math random      Math abs min  max        else           return min   Math random     max            E g    randomBetween -10 15   or   randomBetween 10 20   or    randomBetween -200 -100    Of course  you can also add some validation to make sure you don t do this with anything other than numbers  Also make sure that min is always less than or equal to max

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Math random   is fast and suitable for many purposes  but it s not appropriate if you need cryptographically-secure values  it s not secure   or if you need integers from a completely uniform unbiased distribution  the multiplication approach used in others answers produces certain values slightly more often than others    In such cases  we can use crypto getRandomValues   to generate secure integers  and reject any generated values that we can t map uniformly into the target range  This will be slower  but it shouldn t be significant unless you re generating extremely large numbers of values   To clarify the biased distribution concern  consider the case where we want to generate a value between 1 and 5  but we have a random number generator that produces values between 1 and 16  a 4-bit value   We want to have the same number of generated values mapping to each output value  but 16 does not evenly divide by 5  it leaves a remainder of 1  So we need to reject 1 of the possible generated values  and only continue when we get one of the 15 lesser values that can be uniformly mapped into our target range  Our behaviour could look like this pseudocode   Generate a 4-bit integer in the range 1-16  If we generated  1   6  or 11 then output 1  If we generated  2   7  or 12 then output 2  If we generated  3   8  or 13 then output 3  If we generated  4   9  or 14 then output 4  If we generated  5  10  or 15 then output 5  If we generated 16 then reject it and try again    The following code uses similar logic  but generates a 32-bit integer instead  because that s the largest common integer size that can be represented by JavaScript s standard number type   This could be modified to use BigInts if you need a larger range   Regardless of the chosen range  the fraction of generated values that are rejected will always be less than 0 5  so the expected number of rejections will always be less than 1 0 and usually close to 0 0  you don t need to worry about it looping forever    x000D   x000D  const randomInteger    min  max    gt    x000D    const range   max - min  x000D    const maxGeneratedValue   0xFFFFFFFF  x000D    const possibleResultValues   range   1  x000D    const possibleGeneratedValues   maxGeneratedValue   1  x000D    const remainder   possibleGeneratedValues   possibleResultValues  x000D    const maxUnbiased   maxGeneratedValue - remainder  x000D   x000D    if   Number isInteger min      Number isInteger max     x000D         max  gt  Number MAX SAFE INTEGER    min  lt  Number MIN SAFE INTEGER    x000D      throw new Error  Arguments must be safe integers     x000D      else if  range  gt  maxGeneratedValue    x000D      throw new Error  Range of   range   from   min  to   max    gt    maxGeneratedValue      x000D      else if  max  lt  min    x000D      throw new Error  max    max   must be  gt   min    min       x000D      else if  min     max    x000D      return min  x000D       x000D   x000D    let generated  x000D    do   x000D      generated   crypto getRandomValues new Uint32Array 1   0   x000D      while  generated  gt  maxUnbiased   x000D   x000D    return min    generated   possibleResultValues   x000D     x000D   x000D  console log randomInteger -8  8                -2 x000D  console log randomInteger 0  0                 0 x000D  console log randomInteger 0  0xFFFFFFFF        944450079 x000D  console log randomInteger -1  0xFFFFFFFF    x000D     Error  Range of 4294967296 covering -1 to 4294967295 is  gt  4294967295  x000D  console log new Array 12  fill   map n   gt  randomInteger 8  12     x000D      11  8  8  11  10  8  8  12  12  12  9  9  x000D   x000D   x000D

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for big number  var min num   900  var max num   1000  while true            let num random   Math random    max num      console log  input     num random       if num random  gt   min num           console log Math floor num random           break         else           console log       Math floor num random

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This function can generate a random integer number between  and including  min and max numbers  function randomNumber min  max      if  min  gt  max        let temp   max      max   min      min   temp         if  min  lt   0        return Math floor Math random      max   Math abs min    1     min      else       return Math floor Math random      max - min   1     min         Example  randomNumber -2  3      can be -2  -1  0  1  2 and 3 randomNumber -5  -2      can be -5  -4  -3 and -2 randomNumber 0  4      can be 0  1  2  3 and 4 randomNumber 4  0      can be 0  1  2  3 and 4

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jsfiddle  https   jsfiddle net cyGwf 477   Random Integer  to get a random integer between min and max  use the following code  function getRandomInteger min  max      min   Math ceil min     max   Math floor max     return Math floor Math random      max - min     min      Random Floating Point Number  to get a random floating point number between min and max  use the following code  function getRandomFloat min  max      return Math random      max - min    min      Reference  https   developer mozilla org en-US docs Web JavaScript Reference Global Objects Math random

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Crypto-strong random integer number in range  a b   assumption  a  lt  b     x000D   x000D  let rand   a b   gt  a  b-a 1  crypto getRandomValues new Uint32Array 1   0  2  32 0 x000D   x000D  console log  rand 1 6     x000D   x000D   x000D

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Important  The following code works only if the minimum value is 1  It does not work for minimum values other than 1   If you wanted to get a random integer between 1  and only 1  and 6  you would calculate   Math floor Math random     6    1     Where      1 is the start number     6 is the number of possible results  1   start  6  - end  1

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This should work   const getRandomNum    min  max    gt  Math floor Math random      max - min   1     min

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Math random   Returns an integer random number between min  included  and max  included   function randomInteger min  max      return Math floor Math random      max - min   1     min     Or any random number between min  included  and max  not included   function randomNumber min  max      return Math random      max - min    min     Useful examples  integers      0 - gt  10 Math floor Math random     11       1 - gt  10 Math floor Math random     10    1      5 - gt  20 Math floor Math random     16    5      -10 - gt   -2  Math floor Math random     9  - 10      And always nice to be reminded  Mozilla    Math random   does not provide cryptographically secure random numbers  Do not use them for anything related to security  Use the Web Crypto API instead  and more precisely the window crypto getRandomValues   method

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Try using    x000D   x000D  function random min  max    x000D     return Math round  Math random      Math abs max - min      min   x000D    x000D  console log random 1  6    x000D   x000D   x000D

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ES6   Arrow functions version based on Francis  code  i e  the top answer   const randomIntFromInterval    min  max    gt  Math floor Math random      max - min   1    min

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The top rated solution is not mathematically correct as same as comments under it - gt  Math floor Math random     6    1  Task  generate random number between 1 and 6  Math random   returns floating point number between 0 and 1  like 0 344717274374 or 0 99341293123 for example   which we will use as a percentage  so Math floor Math random     6    1 returns some percentage of 6  max  5  min  0  and adds 1  The author got lucky that lower bound was 1   because percentage floor will  quot maximumly quot  return 5 which is less than 6 by 1  and that 1 will be added by lower bound 1  The problems occurs when lower bound is greater than 1  For instance  Task  generate random between 2 and 6   following author s logic  Math floor Math random     6    2  it is obviously seen that if we get 5 here - gt  Math random     6 and then add 2  the outcome will be 7 which goes beyond the desired boundary of 6  Another example  Task  generate random between 10 and 12   following author s logic  Math floor Math random     12    10   sorry for repeating  it is obvious that we are getting 0 -99  percent of number  quot 12 quot   which will go way beyond desired boundary of 12  So  the correct logic is to take the difference between lower bound and upper bound add 1  and only then floor it  to substract 1  because Math random   returns 0 - 0 99  so no way to get full upper bound  thats why we adding 1 to upper bound to get maximumly 99  of  upper bound   1  and then we floor it to get rid of excess   Once we got the floored percentage of  difference   1   we can add lower boundary to get the desired randomed number between 2 numbers  The logic formula for that will be  Math floor Math random       up boundary - low boundary    1     10  P s   Even comments under the top-rated answer were incorrect  since people forgot to add 1 to the difference  meaning that they will never get the up boundary  yes it might be a case if they dont want to get it at all  but the requirenment was to include the upper boundary

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This works for me and produces values like Python s random randint standard library function    function randint min  max       return Math round  Math random     Math abs max - min     min      console log  Random integer      randint -5  5

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I was searching random number generator written in TypeScript and I have written this after reading all of the answers  hope It would work for TypeScript coders       Rand min  number  max  number   number           return  Math random      max - min   1    0    min

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var x   6     can be any number var rand   Math floor Math random   x    1

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Adding float with fixed precision version based on the int version in  Francisc s answer   function randomFloatFromInterval  min  max  fractionDigits      const fractionMultiplier   Math pow 10  fractionDigits    return Math round       Math random      max - min    min    fractionMultiplier        fractionMultiplier     so   randomFloatFromInterval 1 3 4       gt  2 2679  1 509  1 8863  2 9741        and for int answer  randomFloatFromInterval 1 3 0       gt  1  2  3

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Example  Return a random number between 1 and 10   Math floor  Math random     10    1     The result could be      3  Try yourself  here  --  or using lodash   undescore     random min  max   Docs  - lodash - undescore

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Inspite of many answers and almost same result  I would like to add my answer and explain its working  Because it is important to understand its working rather than copy pasting one line code  Generating random numbers is nothing but simple maths    CODE   function getR lower  upper       var percent    Math random     100        this will return number between 0-99 because Math random returns decimal number from 0-0 9929292 something like that     now you have a percentage  use it find out the number between your INTERVAL  upper-lower    var num     percent    upper - lower    100        num will now have a number that falls in your INTERVAL simple maths   num    lower      add lower to make it fall in your INTERVAL     but num is still in decimal     use Math floor gt downward to its nearest integer you won t get upper value ever     use Math ceil gt upward to its nearest integer upper value is possible     Math round gt to its nearest integer 2 4 gt 2 2 5 gt 3   both lower and upper value possible   console log Math floor num   Math ceil num   Math round num

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TL DR  function generateRandomInteger min  max      return Math floor min   Math random    max   1 - min       To get the random number generateRandomInteger -20  20    EXPLANATION BELOW  We need to get a random integer  say X between min and max   Right    i e  min  lt   X  lt   max  If we subtract min from the equation  this is equivalent to   0  lt    X - min   lt    max - min   Now  lets multiply this with a random number r which is   0  lt    X - min    r  lt    max - min    r  Now  lets add back min to the equation  min  lt   min    X - min    r  lt   min    max - min    r  Now  lets chose a function which results in r such that it satisfies our equation range as  min max   This is only possible if 0 lt   r  lt  1  OK  Now  the range of r i e  0 1  is very similar to Math random   function result  Isn t it      The Math random   function returns a floating-point  pseudo-random   number in the range  0  1   that is  from 0  inclusive  up to but not   including 1  exclusive    For example   Case r   0  min   0    max-min    min  Case r   1  min   1    max-min    max  Random Case using Math random 0  lt   r  lt  1  min   r    max-min    X  where X has range of min  lt   X  lt  max  The above result X is a random numeric  However due to Math random   our left bound is inclusive  and the right bound is exclusive  To include our right bound we increase the right bound by 1 and floor the result   function generateRandomInteger min  max      return Math floor min   Math random    max   1 - min       To get the random number  generateRandomInteger -20  20

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I wrote more flexible function which can give you random number but not only integer   function rand min max interval        if  typeof interval     undefined   interval   1      var r   Math floor Math random    max-min interval  interval       return r interval min     var a   rand 0 10     can be 0  1  2       9  10 var b   rand 4 6 0 1     can be 4 0  4 1  4 2       5 9  6 0   Fixed version

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Other solutions     Math random     6   0    1    Math random     6    1   Try online

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function randomIntFromInterval min  max       min and max included    return Math floor Math random      max - min   1    min       What it does  extra  is it allows random intervals that do not start with 1  So you can get a random number from 10 to 15 for example  Flexibility

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I discovered a great new way to do this using ES6 default parameters  It is very nifty since it allows either one argument or two arguments  Here it is   function random n  b   0        return Math random      b-n    n

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Or  in Underscore    random min  max

[javascript] Generate random number between two numbers in JavaScript

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