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How to Generate Unique ID in JavaScript

Rahman Fadhil on December 22, 2019

Read the original article here There are several ways to generate unique identifier in JavaScript. This could very useful in many cases, such as r...

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Zohar Peled • Dec 22 '19 • Edited

A random number is not the same as a unique number. There is absolutely no guarantee of uniqueness in a collection of randomly generated numbers.

DateTime.Now() will also not generate a unique number, unless guaranteed not to run at the exact same millisecond. for quite a while now, computers are fast enough to run a few iteration of a loop within a single millisecond.

coderkearns • Feb 20 '20

You could decrease the chances by using multiple of the author's ways:

Maybe

function uniqueID() {
return Math.floor(Math.random() * Date.now())
}

You could even string multiple randoms together:

Math.floor(Math.random() * Math.floor(Math.random() * Date.now()))

Ciprian Popescu • Mar 11 '22

Depending on the application, this is the right way to do it. In my case, I don't have a loop, I have several elements being displayed on subsequent clicks, and there's several seconds between each click. So there's zero chances of an identical ID.

abbatyya • Dec 16 '22

thank you, this work also. to also include string i use Math.floor(Math.random() * Date.now()).toString(16)

Mitchell Mortensen • Jun 6 '21

While yes it's theoretically possible for UUID to produce a duplicate, it is statistically improbable (read: impossible) to do so, even when striving for such and taking into account the birthday paradox. According to wikipedia:

"Only after generating 1 billion UUIDs every second for the next 100 years, the probability of creating just one duplicate would be about 50%. Or, to put it another way, the probability of one duplicate would be about 50% if every person on earth owned 600 million UUIDs."
en.wikipedia.org/wiki/Universally_...

You actually more likely to have a totally unique ID than to have gotten one that anyone has ever seen in the entire world! And it will be this way until the sun runs out of juice.

UUID is the only one that should be used. Date.now() is terrible for reasons that Zohar mentions.

Rahman Fadhil • Dec 22 '19

I kind of agree 🤔

I think the title should be "how to generate random id"

But, at least I put UUID as the most recommended approach

Zohar Peled • Dec 23 '19

In fact, random numbers probability of uniqueness is actually a lot smaller than what one can expect, without knowledge of what's called the birthday problem.

In a nutshell - Take a group of random people. What are the chances two of them was born in the same date (day and month, year not included)?

Turns out, that if the group contains 32 people, that chance is 50%. With 70 people in the group, its 99.9%.

So the chances of getting the same random number twice when your range is between 0 and 100 increase rapidly the larger the group is.

Siddharth • Sep 19 '21

I just tried the Date.now() method, and even when I ran a loop 1000 times, all the "unique" numbers were the same.

Caelin Limerick • Sep 14 '23

That's because it all ran within the same millisecond. Date.now() returns time since epoch in ms, so if you run it twice within 1ms the number will be the same since the time since epoch in ms is the same. This is why UUID is a much better approach (like literally the best, universally agreed on approach) however you can still fix this by adding a 1ms delay in your loop, or doing something like multiply by math.random() to add some varation.

Siddharth • Sep 14 '23

Yeah that's right!

Also, UUID is slowly being replaced by NanoID - it's faster, smaller (both package size and IDs), URL friendly, and cryptographically more secure (although both of them are secure enough for that to be irrelevant)

Joe Buckle • Dec 22 '19

UUID is the goto solution for JS at least.

Rob Levin • May 23 '22

I was researching this and while I agree uuid package is probably least human error prone, it does mean potentially adding another package.

It seems like utilizing Date.now().toString or perhaps new Date().getTime() or similar and also Math.random could do the trick:

const uid = () =>
  String(
    Date.now().toString(32) +
      Math.random().toString(16)
  ).replace(/\./g, '')

We can test it by adding generated to a map and comparing size:

const size = 1000000
const set = new Set(new Array(size)
  .fill(0)
  .map(() => uid()))

console.log(
  size === set.size ? 'all ids are unique' : `not unique records ${size - set.size}`
)

Gregori Piñeres • Mar 6 '23

Your script now are in my personal helpers file. thanks.

Justin Golden • May 30 '22

This is the best comment here, and with only one like! A perfect small utility and a way to test it, all super intuitive and functional : )

Sujal Shah • Jul 7 '23

There is 1 inbuilt method which returns randomUUID
window.crypto.randomUUID()

No 3rd party library, Super fast ⌛

Mohamed Johnson • Apr 20 '23

For anyone trying out the first example with uuid, it works just fine and the module respects the standards, it just evolved and I guess the post did not 😅.
Anyhow here's the correct implementation

import { v4 as uuidv4 } from 'uuid';
uuidv4(); // ⇨ '9b1deb4d-3b7d-4bad-9bdd-2b0d7b3dcb6d'

// ... or using CommonJS syntax:
const { v4: uuidv4 } = require('uuid');
uuidv4(); // ⇨ '1b9d6bcd-bbfd-4b2d-9b5d-ab8dfbbd4bed'

Feel free to test it out ^^

Gui • Jan 20 '23 • Edited

It's my way to generate a 100% guaranted unique and random local id:

var MyLib = {
    //Max id guaranted to be unique will be 999 999 999. 
    //Add more zeros to increase the value.
    lastUid : 100000000, 

    generateUid : function(){
        this.lastUid++;

        //Way to get a random int value betwen min and max: 
        //Math.floor(Math.random() * (max - min) ) + min;
        var randValue = Math.floor(Math.random() * (99999 - 10000)) + 10000;

        return Number(this.lastUid.toString() + randValue);
    }
};

console.log(MyLib.generateUid());

Blend_Smile • Jun 30 '20 • Edited

i never think of using millisecond to generate an id, nice approach!

greetings from indonesia :)

Uriel Bitton • May 4 '21

Math.random does neither generate truly random numbers nor are they unique. Its randomness is of course based on the range you provide and that is its own shortcoming. The other methdos you mentioned are a lot more unique and more random.
Cheers!

Pavel Fedotov • Apr 5

The Math.random() static method returns a floating-point, pseudo-random number that's greater than or equal to 0 and less than 1, with approximately uniform distribution over that range — which you can then scale to your desired range. The implementation selects the initial seed to the random number generation algorithm; it cannot be chosen or reset by the user.

developer.mozilla.org/en-US/docs/W...

pranay rauthu • Dec 22 '19

Check my article related to uuid in JavaScript

dev.to/pranay_rauthu/uuid-in-javas...

Rahman Fadhil • Dec 23 '19

Wow, great article 🤩

Bruno Dantas • Mar 4 '20

I was building a local db with npmjs.com/package/lowdb just for testing purposes and the Date.now() is more than enough to get an unique id. Thanks Rahman :)