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How to Generate Unique ID in JavaScript

Abdurrahman 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.

Abdurrahman 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

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 ^^

Blend_Smile • Jun 30 '20 • Edited

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

greetings from indonesia :)

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());

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!

Erick Otieno Awino • Nov 22 '24 • Edited

how about using crypto.randomUUID(), which is part of the Web Crypto API that generates a UUIDv4. I read that it is fast, secure, and simple to use. Here is an example:
const uuid = crypto.randomUUID(); console.log (uuid); // a random and unique ID.

Rohan Sawant • Dec 22 '19

What a great read!

🔥

pranay rauthu • Dec 22 '19

Check my article related to uuid in JavaScript

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

Abdurrahman 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 :)

Pavel Fedotov • Apr 5 '24

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...