*Read the original article here*

There are several ways to generate unique identifier in JavaScript. This could very useful in many cases, such as rendering list efficiently, or storing documents or records in database.

## Using UUID

UUID is the abbreviation of univerally unique identifier, which is an identification number to uniquely identify something. The main idea of this thing is everytime we generate this numbers, it will be **universally** unique, which means no one could generate the exact same id as yours.

I personally prefer this approach in any case. In JavaScript, we can use a library called `uuid`

to generate UUID.

```
$ npm install uuid
```

```
const uuidv4 = require("uuid/v4")
uuidv4()
```

UUID has several versions, but the version that appropriate for generating unique id is version 4. And, that code will generate something like this.

```
1b9d6bcd-bbfd-4b2d-9b5d-ab8dfbbd4bed
```

## Using Math.random

Math.random is a JavaScript built-in function which allows us to generate a random number. Which means that everytime we run it, it will return a unique combination of numbers.

```
Math.floor(Math.random() * 100)
```

`Math.random`

always returns a decimal number, so we need to rounding off that number first. By multiply it with 100, it will return any number between 0 to 99. You can increase the number if you want to get better result.

Result:

```
52
```

## Using Date.now

Date.now is another JavaScript built-in function which allows us to get the number of miliseconds elapsed since January 1, 1970.

```
Date.now()
```

Result:

```
1576996323453
```

## Top comments (29)

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.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()))

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.

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

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.

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

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.

I just tried the

`Date.now()`

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

UUID is the goto solution for JS at least.

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

__

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

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 : )

There is 1 inbuilt method which returns randomUUID

`window.crypto.randomUUID()`

No 3rd party library, Super fast ⌛

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

Feel free to test it out ^^

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

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

greetings from indonesia :)

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!

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...

What a great read!

🔥

Check my article related to uuid in JavaScript

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

Wow, great article 🤩

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 :)

Thanks, this is useful

I think UUID as the most recommended approach

nice! Date.now() good resolve

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