generate random UUIDs

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.

There's also @LeverOne's approach using iteration, which is one byte shorter.

annotated.js

function b(
  a                  // placeholder
){
  return a           // if the placeholder was passed, return
    ? (              // a random number from 0 to 15
      a ^            // unless b is 8,
      Math.random()  // in which case
      * 16           // a random number from
      >> a/4         // 8 to 11
      ).toString(16) // in hexadecimal
    : (              // or otherwise a concatenated string:
      [1e7] +        // 10000000 +
      -1e3 +         // -1000 +
      -4e3 +         // -4000 +
      -8e3 +         // -80000000 +
      -1e11          // -100000000000,
      ).replace(     // replacing
        /[018]/g,    // zeroes, ones, and eights with
        b            // random hex digits
      )
}

index.js

function b(a){return a?(a^Math.random()*16>>a/4).toString(16):([1e7]+-1e3+-4e3+-8e3+-1e11).replace(/[018]/g,b)}

LICENSE.txt

            DO WHAT THE FUCK YOU WANT TO PUBLIC LICENSE
                    Version 2, December 2004

 Copyright (C) 2011 Jed Schmidt <http://jed.is>

 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 WHAT THE FUCK YOU WANT TO PUBLIC LICENSE
   TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION

  0. You just DO WHAT THE FUCK YOU WANT TO.

package.json

{
  "name": "UUID",

  "description": "Generates random UUIDs",

  "keywords": [
    "UUID",
    "ID",
    "random" 
  ]
}

We can use coercion and exponential notation to get template string and save 7 bytes:
function(){return(""+1e7+-1e3+-4e3+-8e3+-1e11).replace(/1|0/g,function(){return(0|Math.random()*16).toString(16)})}

subzey, you are a genius. fixing and annotating now.

you also inspired me to cut 10 more bytes out:

function b(a){return a?(0|Math.random()*16).toString(16):(""+1e7+-1e3+-4e3+-8e3+-1e11).replace(/1|0/g,b)}

(0|Math.random()*16).toString(16)

can also be trimmed 4 bytes to

Math.random().toString(16)[2]

if you don't care about IE... thoughts?

@jed, Math.random() may return 0, so Math.random().toString(16)[2] may return undefined.

Also, isn't setting name of function affects the outer scope?

well, with the chance of Math.random returning a zero 1 in 2<<61, seems like the definition of an edge case. more likely that IE barfs on it.

also, we're allowing named functions because we assume that they'll be assigned externally.

@jed, thanks for your clarification about function names, I didn't know that

@subzey, i hope you use this knowledge to bring us some awesome new stuff.

""+1e7+-1e3+-4e3+-8e3+-1e11 --> [1e7]+-1e3+-4e3+-8e3+-1e11
it's а flaw of many of you.

@LeverOne, perfect! Thanks

wow, that's crazy. good work @LeverOne.

What about replacing /1|0/ with /\d/?

the 4 is hardcoded according to the spec, and the 8 is a bit of a hack... technically it should be anything from 8 to b. so replacing those would make it less compliant.

Ah I see, I missed that.

i wonder if we finally have enough bytes to make it compliant, such that the 8 can be 8, 9, a, or b...

It is enough already :)

function c(a,b){return a?(~~b+0|Math.random()*16>>b/4).toString(16):([1e7]+-1e3+-4e3+-8e3+-1e11).replace(/1|0|(8)/g,c)}

Or this, shorter:

function c(a,b){return a?(b|Math.random()*16>>b/4).toString(16):([1e7]+-1e3+-4e3+-8e3+-1e11).replace(/1|0|(8)/g,c)}

thanks again, @subzey. updated.

Line 20 of annotated.js should be 'c', not 'b'.

BTW, you're all insane. I love it! :)

good catch! for those not in the know, @broofa is a celebrity in the world of UUIDs: https://github.com/broofa/node-uuid

Maybe save 4 bytes...?
```function c(a){return a?(a^Math.random()*16>>a/4).toString(16):([1e7]+-1e3+-4e3+-8e3+-1e11).replace(/[108]/g,c)}

what the... how on earth does this work?

There are three possible values 0,1,8 for a.

For case 0: 0^Math.random()*16>>0/4, >>0/4 is actually >>0, just works as Math.floor.
The 0^ here does nothing.

For case 1: 1^Math.random()*16>>1/4, >>1/4 is still >>0.
Although 1^ here toggles the least significant bit, we can still use it to generate random numbers 0-15.

For case 8: 8^Math.random()*16>>8/4, >>8/4 turns out >>2.
The maximum number of Math.random()*16 in binary form is 1111, that means the range is 0000-1111.
By right shifting 2 bits, the maximum number of Math.random()*16>>2 is 0011, and the range, 0000-0011. What it does here is to generate random numbers 0-3.
Finally, because the most significant bit is always 0, 8^ is actually 8|, it is to ensure the range starts from 8. And now we get 8 + {0, 1, 2, 3}.

incredible work, @tsaniel!

it's amazing how this gist has evolved, from

function(){return"00000000-0000-4000-8000-000000000000".replace(/0/g,function(){return(0|Math.random()*16).toString(16)})}

to

function b(a){return a?(a^Math.random()*16>>a/4).toString(16):([1e7]+-1e3+-4e3+-8e3+-1e11).replace(/[018]/g,b)}

while hitting all the greatest hits: recursion, coercion of a number into a string through an array (!), operator repurposing...

I love those tricks, especially the string coercion with array, though i love bitwise tricks.
By the way, i am still thinking if we can shorten /[018]/...

@tsaniel - no way, the other way round would be /[^4-]/, which is just as long.

@atk: That's true. I mean if we can do something to use /\d/ instead.

...which would require that the 4 will be left alone and enlarge the equation probably more than the 3 letters we saved.

Maybe that's the end.

I fear it is.

Once again, excellent work, @tsaniel!

Sorry for my late comment, my mobile browser doesn't work well with github

Recursion & coercion vs. loop & math: https://gist.github.com/1308368

just when you thought it couldn't get any shorter, @LeverOne sheds a byte. good job!

@LeverOne is my hero.

damnit jed, i keep finding you everywhere. thanks for this!

In Firefox you could use the single statement function body to shorten it a few bits still:

function b(a)a?(a^Math.random()*16>>a/4).toString(16):([1e7]+-1e3+-4e3+-8e3+-1e11).replace(/[018]/g,b)

Shorter yet (cheats, ES6, and works only in Firefox!!!), and less leaky:

function()([1e7]+-1e3+-4e3+-8e3+-1e11).replace(/[018]/g,a=>(a^Math.random()*16>>a/4).toString(16))

Hah, since I already used ES6 and there are no variable assignments, might as well go all the way and avoid Firefox-only stuff:

()=>([1e7]+-1e3+-4e3+-8e3+-1e11).replace(/[018]/g,a=>(a^Math.random()*16>>a/4).toString(16))

This is awesome!

Here's a benchmark vs node-uuid: http://jsperf.com/node-uuid-performance/11

I was so rooting for Crazy Gist to win that one :(

Is this relatively safe to generate UUIDs simultaneously between many clients?

Make it secure at the cost of just a few bytes by replacing Math.random() * 16:

browser

crypto.getRandomValues(new Uint8Array(1))[0] % 16

function b(
  a                  // placeholder
){
  return a           // if the placeholder was passed, return
    ? (              // a random number from 0 to 15
      a ^            // unless b is 8,
      crypto.getRandomValues(new Uint8Array(1))[0]  // in which case
      % 16           // a random number from
      >> a/4         // 8 to 11
      ).toString(16) // in hexadecimal
    : (              // or otherwise a concatenated string:
      [1e7] +        // 10000000 +
      -1e3 +         // -1000 +
      -4e3 +         // -4000 +
      -8e3 +         // -80000000 +
      -1e11          // -100000000000,
      ).replace(     // replacing
        /[018]/g,    // zeroes, ones, and eights with
        b            // random hex digits
      )
}

node.js

crypto.randomBytes(1)[0] % 16

function b(
  a                  // placeholder
){
  return a           // if the placeholder was passed, return
    ? (              // a random number from 0 to 15
      a ^            // unless b is 8,
      crypto.randomBytes(1)[0]  // in which case
      % 16           // a random number from
      >> a/4         // 8 to 11
      ).toString(16) // in hexadecimal
    : (              // or otherwise a concatenated string:
      [1e7] +        // 10000000 +
      -1e3 +         // -1000 +
      -4e3 +         // -4000 +
      -8e3 +         // -80000000 +
      -1e11          // -100000000000,
      ).replace(     // replacing
        /[018]/g,    // zeroes, ones, and eights with
        b            // random hex digits
      )
}

@coolaj89 I don't have crypto.randomBytes in Chrome 46.0.2490.80 but there is crypto.getRandomValues

And even smaller now:

b = a=>a?(a^Math.random()*16>>a/4).toString(16):([1e7]+-1e3+-4e3+-8e3+-1e11).replace(/[018]/g,b);