How can I generate random number between number A and number B in javascript ?

For stronger randomness (useful for security tokens, password generators or games), JavaScript provides a built-in Crypto API.
This API produces random values that are much harder to predict than Math.random().

function cryptoRandom(a, b) {
  const rand = crypto.getRandomValues(new Uint32Array(1))[0] / 2 ** 32;
  return Math.floor(rand * (b - a + 1)) + a;
}

Example:

console.log(cryptoRandom(1000, 9999)); // Output: Secure random integer between 1000 and 9999 

How it works:

• crypto.getRandomValues() uses the operating system’s secure random number generator.
• Dividing by 2 ** 32 normalizes the number to a range between 0 and 1.
• The rest of the math is similar to the standard version, it scales and shifts the value between a and b.

Using window.crypto.randomUUID() (for unique random identifiers)

While not for numbers directly, it can be used to generate unique random strings and you can extract numeric parts.

Example:

const id = crypto.randomUUID(); 
console.log(id); // "3f4a0b8b-23f1-4e99-bcf3-8f9a7b8413cd" 

You can convert a portion of it to a number if needed:

const num = parseInt(id.replace(/-/g, '').slice(0, 8), 16);

Use this for: generating random unique IDs, order numbers or tracking codes.

use Nanoid for Fast and secure random number generation

npm install nanoid

import { nanoid } from 'nanoid';

console.log(nanoid());     // e.g. "V1StGXR8_Z5jdHi6B-myT" (21 chars) 
console.log(nanoid(10));   // e.g. "kE93sdPqW1" (10 chars) 

Use for: unique IDs, file names, sessions, database keys. It is Fast, secure and URL-safe random ID generator.

For random number generation can use below code

import { nanoid } from 'nanoid';

// Generate a random numeric ID (only digits)
function nanoidNumber(length = 6) {
  const digits = '0123456789';
  return Array.from({ length }, () => digits[Math.floor(Math.random() * 10)]).join('');
}
// Example usage
console.log(nanoidNumber());    // e.g. "583920"
console.log(nanoidNumber(10));  // e.g. "3847569201"

Using Date.now() and Random Modifiers

Not truly random, but sometimes used for pseudo-random values when seeding or generating IDs.

Example:

function timeBasedRandom(a, b) {
  const rand = (Date.now() % 1000) / 1000;
  return Math.floor(rand * (b - a + 1)) + a;
}

Use this for: temporary identifiers or quick unique values (not secure).

Custom Random Generator (Using Seeds)

If you want reproducible randomness (same output every time using the same seed), use a seeded random function.

 Example:

function seededRandom(seed, a, b) {
  const x = Math.sin(seed++) * 10000;
  const rand = x - Math.floor(x);
  return Math.floor(rand * (b - a + 1)) + a;
}

 Use this for: simulations, games or tests where you need predictable random sequences.

Using External Libraries (More Options & Control)

Several libraries provide advanced randomization features. you can use any Library to generate a high quality random value.

Libraries that you can use:

• Lodash – Simple and reliable random number generator for integers and floats.
• Chance.js – Powerful library for generating random numbers, strings and fake data.
• Random.js – Advanced random number generator with seeding and distribution support.
• Seedrandom – Deterministic random generator that allows reproducible randomness via seeds.
• Crypto-random-string – Generates cryptographically secure random strings.
• @faker-js/faker – Creates realistic fake data (names, emails, numbers etc.) for testing.
• Nanoid – Tiny, secure and fast library for generating unique random IDs.
• Randomatic – Generates random strings, numbers or patterns with custom masks.
• Random-seed – Lightweight library for creating multiple seeded random number generators.
• UUID / crypto.randomUUID() – Built-in secure random UUID generator for unique identifiers.

Example with Lodash:

// Install Lodash: npm install lodash 
import { random } from "lodash";

console.log(random(5, 15));        // random integer between 5 and 15 
console.log(random(5, 15, true));  // random float between 5 and 15 

Use this for: convenience and better readability in larger projects.