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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 (25)

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.

This one is very very helpful than a post 😄 Thanks Buddy 😇

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 just tried the

`Date.now()`

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

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 : )

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

greetings from indonesia :)

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

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!

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 :)

What a great read!

🔥

Check my article related to uuid in JavaScript

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

Wow, great article 🤩

I think UUID as the most recommended approach

nice! Date.now() good resolve

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