Random alpha-numeric string in JavaScript

Question

What s the shortest way  within reason  to generate a random alpha-numeric  uppercase  lowercase  and numbers  string in JavaScript to use as a probably-unique identifier

User · Answer

I just came across this as a really nice and elegant solution:

Math.random().toString(36).slice(2)

Notes on this implementation:

This will produce a string anywhere between zero and 12 characters long, usually 11 characters, due to the fact that floating point stringification removes trailing zeros.
It won't generate capital letters, only lower-case and numbers.
Because the randomness comes from Math.random(), the output may be predictable and therefore not necessarily unique.
Even assuming an ideal implementation, the output has at most 52 bits of entropy, which means you can expect a duplicate after around 70M strings generated.

User · Answer

Or to build upon what Jar Jar suggested  this is what I used on a recent project  to overcome length restrictions    var randomString   function  len  bits        bits   bits    36      var outStr       newStr      while  outStr length  lt  len                newStr   Math random   toString bits  slice 2           outStr    newStr slice 0  Math min newStr length   len - outStr length               return outStr toUpperCase         Use   randomString 12  16      12 hexadecimal characters randomString 200      200 alphanumeric characters

User · Answer

When I saw this question I thought of when I had to generate UUIDs  I can t take credit for the code  as I am sure I found it here on stackoverflow  If you dont want the dashes in your string then take out the dashes  Here is the function   function generateUUID         var d   new Date   getTime        var uuid    xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx  replace   xy  g function c            var r    d   Math random   16  16   0          d   Math floor d 16           return  c   x    r    r amp 0x7 0x8   toString 16               return uuid toUpperCase        Fiddle  http   jsfiddle net nlviands fNPvf 11227

User · Answer

Random character   String fromCharCode i     where is an int   Random int   Math floor Math random   100     Put it all together   function randomNum hi       return Math floor Math random   hi      function randomChar        return String fromCharCode randomNum 100      function randomString length      var str          for var i   0  i  lt  length    i           str    randomChar            return str    var RandomString   randomString 32     32 length string   Fiddle  http   jsfiddle net maniator QZ9J2

User · Answer

UPDATED  One-liner solution  for random 20 characters  alphanumeric lowercase   Array from Array 20        gt  Math floor Math random     36  toString 36   join       Or shorter with lodash    times 20       gt    random 35  toString 36   join

User · Answer

function randomString len        var p    ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789       return     Array len   reduce a  gt a p    Math random   p length            Summary         Create an array of the size we want  because there s no range len  equivalent in javascript    For each element in the array  pick a random character from p and add it to a string   Return the generated string       Some explanation       Array len    Array len  or new Array len  creates an array with undefined pointer s    One-liners are going to be harder to pull off   The Spread syntax conveniently defines the pointers  now they point to undefined objects      reduce   Reduce the array to  in this case  a single string  The reduce functionality is common in most languages and worth learning    a  gt a       We re using an arrow function   a is the accumulator  In this case it s the end-result string we re going to return when we re done  you know it s a string because the second argument to the reduce function  the initialValue is an empty string        So basically  convert each element in the array with p    Math random   p length    append the result to the a string and give me a when you re done   p       p is the string of characters we re selecting from   You can access chars in a string like an index  E g    abcdefg  3  gives us  d       Math random   p length   Math random   returns a floating point between  0  1  Math floor Math random   max  is the de facto standard for getting a random integer in javascript    is the bitwise NOT operator in javascript       is a shorter  arguably sometimes faster  and definitely funner way to say Math floor  Here s some info

User · Answer

Using lodash    x000D   x000D  function createRandomString length    x000D          var chars    abcdefghijklmnopqrstufwxyzABCDEFGHIJKLMNOPQRSTUFWXYZ1234567890  x000D          var pwd     sampleSize chars  length    12      lodash v4  use   sampleSize x000D          return pwd join     x000D        x000D  document write createRandomString 8   x000D   lt script src  https   cdnjs cloudflare com ajax libs lodash js 4 17 11 lodash min js  gt  lt  script gt  x000D   x000D   x000D

User · Answer

This is cleaner  Math random   toString 36  substr 2  length    Example  Math random   toString 36  substr 2  5

User · Answer

for 32 characters   for var c       c length  lt  32   c    Math random   toString 36  substr 2  1

User · Answer

This function should give a random string in any length   function randString length        var l   length  gt  25   25   length      var str   Math random   toString 36  substr 2  l       if str length  gt   length           return str            return str concat this randString length - str length        I ve tested it with the following test that succeeded   function test        for var x   0  x  lt  300000  x             if randString x  length    x               throw new Error  invalid result for len     x                       The reason i have chosen 25 is since that in practice the length of the string returned from Math random   toString 36  substr 2  25  has length 25  This number can be changed as you wish   This function is recursive and hence calling the function with very large values can result with Maximum call stack size exceeded  From my testing i was able to get string in the length of 300 000 characters   This function can be converted to a tail recursion by sending the string to the function as a second parameter  I m not sure if JS uses Tail call optimization

User · Answer

Use md5 library  https   github com blueimp JavaScript-MD5  The shortest way   md5 Math random     If you want to limit the size to 5   md5 Math random    substr 0  5

User · Answer

Another variation of answer suggested by JAR JAR beans   Math random   1e32  toString 36    By changing multiplicator 1e32 you can change length of random string

User · Answer

I think the following is the simplest solution which allows for a given length   Array myLength  fill 0  map x   gt  Math random   toString 36  charAt 2   join       It depends on the arrow function syntax

User · Answer

Nice and simple  and not limited to a certain number of characters   let len   20  str       while str length  lt  len  str    Math random   toString 36  substr 2   str   str substr 0  len

User · Answer

var randomString   function length      var str         var chars   0123456789ABCDEFGHIJKLMNOPQRSTUVWXTZabcdefghiklmnopqrstuvwxyz  split               var charsLen   chars length    if   length        length      Math random     charsLen         for  var i   0  i  lt  length  i          str    chars    Math random     charsLen          return str

User · Answer

Random Key Generator  keyLength argument is the character length you want for the key  function keyGen keyLength        var i  key       characters    abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789        var charactersLength   characters length       for  i   0  i  lt  keyLength  i              key    characters substr Math floor  Math random     charactersLength    1   1              return key      keyGen 12   QEt9mYBiTpYD

User · Answer

If you only want to allow specific characters  you could also do it like this   function randomString length  chars        var result           for  var i   length  i  gt  0  --i  result    chars Math floor Math random     chars length        return result    var rString   randomString 32   0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ      Here s a jsfiddle to demonstrate  http   jsfiddle net wSQBx   Another way to do it could be to use a special string that tells the function what types of characters to use  You could do that like this   function randomString length  chars        var mask           if  chars indexOf  a    gt  -1  mask     abcdefghijklmnopqrstuvwxyz       if  chars indexOf  A    gt  -1  mask     ABCDEFGHIJKLMNOPQRSTUVWXYZ       if  chars indexOf       gt  -1  mask     0123456789       if  chars indexOf       gt  -1  mask              amp      -           lt  gt               var result           for  var i   length  i  gt  0  --i  result    mask Math floor Math random     mask length        return result     console log randomString 16   aA     console log randomString 32    aA     console log randomString 64    A        Fiddle  http   jsfiddle net wSQBx 2   Alternatively  to use the base36 method as described below you could do something like this   function randomString length        return Math round  Math pow 36  length   1  - Math random     Math pow 36  length    toString 36  slice 1

[javascript] Random alpha-numeric string in JavaScript?

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