var id = "id" + Math.random().toString(16).slice(2)

const uid = function(){
    return Date.now().toString(36) + Math.random().toString(36).substr(2);
}

This Function generates very unique IDs that are sorted by its generated Date. Also useable for IDs in Databases.

No external libraries needed. Uniqueness proved.

You could do something like this.

// Function to generate unique id

const uniqueId = (length=16) => {
  return parseInt(Math.ceil(Math.random() * Date.now()).toPrecision(length).toString().replace(".", ""))
}

// ----------------------------

document.querySelector("#butt01").onclick = () => {
  document.querySelector("#span01").innerHTML = uniqueId()
}

ids = []
count = 0
document.querySelector("#butt02").onclick = () => {
  for (let i = 0; i< 1000; i++){
    ids.push(uniqueId())
  }
  for (el of ids){
    for (ell of ids){
      if(el == ell && ids.indexOf(el) != ids.indexOf(ell)){
        count += 1
      }
    }
  }
  document.querySelector("#span02").innerHTML = `Found ${count} duplicated random values.`
}

<button id="butt01">Generate</button>
<br>
<span id="span01"></span>
<br>
<hr>
<br>
<button id="butt02">Check collision potentiality in 1000 cases</button>
<br>
<span id="span02"></span>

Multiply time in milliseconds since epoch with a random value to fixed size.

Run this to see possible collisions.

You would see there are no collisions whether it is 1000, 10000 or 1000000000.

It would have a very small chance if two users generate ids at the same time and gets the rame random number.

To increase the uniqueness you could multiply date more Math.random()s.

You can use the Generator function, was introduced in ES6 (https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/function*)

const idCreator = function* () {
    let i = 0;
    while (true) yield i++;
};

const idsGenerator = idCreator();
const generateId = () => idsGenerator.next().value;

console.log(generateId()) // 0
console.log(generateId()) // 1
console.log(generateId()) // 2
...

There are two packages available for this.

• For short unique id generation nanoid link

import { nanoid } from 'nanoid'
const id = nanoid()    // "Uakgb_J5m9g-0JDMbcJqLJ"
const id = nanoid(10)  // "jcNqc0UAWK"

• For universally unique id generation uuid link

import { v4 as uuidv4 } from 'uuid';
const id= uuidv4();    // quite big id

The shortest and without libraries, also works in nodejs

crypto.randomUUID();
// 'a63ae209-ec69-4867-af8a-6f4d1efe15c6'

https://developer.mozilla.org/en-US/docs/Web/API/Crypto/randomUUID

btn.onclick = () => myID.textContent = crypto.randomUUID()

<button id="btn">Generate ID</button>
<myID id="myID"></myID>

Random is not unique. Times values are not unique. The concepts are quite different and the difference rears its ugly head when your application scales and is distributed. Many of the answers above are potentially dangerous.

A safer approach to the poster's question is UUIDs: Create GUID / UUID in JavaScript?

function generateId() {
       
  return Math.random().toString(36).substring(2) +
    (new Date()).getTime().toString(36);
}

console.log(generateId())

Look at this functions, it will get ur job done.

If u want uppercase and lowercase chars in ur string:

function (length) {
    var id = '';
            while (id.length < length) {
                var ch = Math.random()
                    .toString(36)
                    .substr(2, 1);
                if (Math.random() < 0.5) {
                    ch = ch.toUpperCase();
                }
                id += ch;
            }
            return id;
}

Only lowercase chars:

function (length) {
    var id = '';
            while (id.length < length) {
                id += Math.random()
                    .toString(36)
                    .substr(2, 1);
            }
            return id;
}

Simple Solution :)

const ID = (_length=13) => {
  // Math.random to base 36 (numbers, letters),
  // grab the first 9 characters
  // after the decimal.
  return '_' + Math.random().toString(36).substr(2, _length); // max _length should be less then 13
};
console.log("Example ID()::", ID())

Just two cents

function makeId(tokenLen) {
    if (tokenLen == null) {
        tokenLen = 16;
    }
    var text = "";
    const possible = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789";
    for (var i = 0; i < tokenLen; ++i)
        text += possible.charAt(Math.floor(Math.random() * possible.length));

    return text;
}

Combining random & date in ms should do the trick with almost no change of collision :

function uniqid(){
  return Math.random().toString(16).slice(2)+(new Date()).getTime()+Math.random().toString(16).slice(2);
}
alert(uniqid()+"\r"+uniqid());

    const generateUniqueId = () => 'id_' + Date.now() + String(Math.random()).substr(2);

    // if u want to check for collision
    const arr = [];
    const checkForCollision = () => {
      for (let i = 0; i < 10000; i++) {
        const el = generateUniqueId();
        if (arr.indexOf(el) > -1) {
          alert('COLLISION FOUND');
        }
        arr.push(el);
      }
    };

I think if you really want to have a unique ID then the best approach is to use a library like:
uuid or uniqueid

Note: Unique ID is not the same as Random ID

To use only date time milliseconds approach is wrong.
Nowadays computers are fast enough and able to run more than one iteration of a loop in a single millisecond.

npm install uuid

Importing the library:

If you are using ES modules

import { v4 as uuidv4 } from 'uuid';

And for CommonJS:

const { v4: uuidv4 } = require('uuid');

Usage:

uuidv4();

// This will output something like: 9b1deb4d-3b7d-4bad-9bdd-2b0d7b3dcb6d

For generate unique id's:

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

For check that is works:

var size = 500000
var arr = new Array(size)
  .fill(0)
  .map(() => uid())

var b = new Set(arr)

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

I managed to have a non digit unique id with this function, so i'll like to share :)

const id = btoa((Math.random(0,(new Date()).getTime())).toString()).slice(0, -10);

I sliced it for DB varchar limit reasons, but you're free to do without it.

let transactionId =${new Date().getDate()}${new Date().getHours()}${new Date().getSeconds()}${new Date().getMilliseconds()}

let transactionId =`${new Date().getDate()}${new Date().getHours()}${new Date().getSeconds()}${new Date().getMilliseconds()}` 

console.log(transactionId)