Generate unique random numbers in javascript or typescript

There are many examples around internet. You can start with using Math.random() . For example: generate random number between 1 and 100

Math.floor((Math.random() * 100) + 1);

Just keep in mind that it is not truly random; it is not cryptographically secure. You should probably look into libraries if you need that

Create a function that returns a unique number:

let numbers = [];

const uniqueNumber = (maxVal) => {
   const number = Math.floor((Math.random() * maxVal) + 1);
   if (!numbers.includes(number)) {
      numbers.push(number);
      return number;
   } else if (numbers.length - 1 !== maxVal) {
      uniqueNumber(maxVal);
   }
}

const randomNumber = uniqueNumber(100);
console.log(numbers) // returns all unique numbers

This will return a unqiue number between 1 and 100. It also stops at the max length.

You can use the package uuid:

const uuidv4 = require('uuid/v4');
uuidv4(); // ⇨ '10ba038e-48da-487b-96e8-8d3b99b6d18a'

Notice: It is a number (a 128-bit number) but it is too big to be used as a JavaScript number. You have to keep it as a string.

If you need it on the browser, I suggest to generate the identifier from an API exposed on your back-end. Implementations of UUID exist in most of languages. The npm package will work on browsers but then it uses a fallback to Math.random, which is not secure.

See also: Universally unique identifier.

var datetimestamp = Date.now() + Math.random().toString(36).substr(2, 9);

1. Math.random() in itself should be safe enough, what with 64-bit numbers. Even with imperfect generator, the chances of hitting the same number twice are minuscule.

2. If you're after specifically integers, then multiply Math.random() by something BIG, like Number.MAX_SAFE_INTEGER.

3. To be perfectly safe, you can always store an array of already used ids, and write a function that draws as long as gets a new unique number, pushes it into array, and returns the value. Enclose all that functionality inside a single object/function/class, to keep it neat.