generate random v4 UUIDs (107 bytes)

README.md

UUID

Returns a random v4 UUID of the form xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx, where each x is replaced with a random hexadecimal digit from 0 to f, and y is replaced with a random hexadecimal digit from 8 to b.

Instance, based on recursion, can be found here.

annotated.js

function(
  a,b                // placeholders
){
  for(               // loop :)
      b=a='';        // b - result , a - numeric variable
      a++<36;        // 
      b+=a*51&52  // if "a" is not 9 or 14 or 19 or 24
                  ?  //  return a random number or 4
         (
           a^15      // if "a" is not 15
              ?      // genetate a random number from 0 to 15
           8^Math.random()*
           (a^20?16:4)  // unless "a" is 20, in which case a random number from 8 to 11
              :
           4            //  otherwise 4
           ).toString(16)
                  :
         '-'            //  in other cases (if "a" is 9,14,19,24) insert "-"
      );
  return b
 }

index.js

function(a,b){for(b=a='';a++<36;b+=a*51&52?(a^15?8^Math.random()*(a^20?16:4):4).toString(16):'-');return b}

LICENSE.txt

            DO WTF YOU WANT TO PUBLIC LICENSE
                    Version 2, December 2004

 Copyright (C) 2011 Alexey Silin <[email protected]>

 Everyone is permitted to copy and distribute verbatim or modified
 copies of this license document, and changing it is allowed as long
 as the name is changed.

            DO WTF YOU WANT TO PUBLIC LICENSE
   TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION

  0. You just DO WTF YOU WANT TO.

package.json

{
  "name": "UUID",

  "description": "Generates random UUIDs",
  "contributors": [
    "jed",
    "subzey",
    "tsaniel"
  ],
  "keywords": [
    "UUID",
    "ID",
    "random" 
  ]
}

@LiamKarlMitchell You have an extra ) at the end of your function. You can save another byte 😄