Rounding

// round up
Math.ceil

// round down
Math.floor 

Math.random()

static method returns a floating-point, pseudo-random number that's greater than or equal to 0 and less than 1

• approximately uniform distribution over that range
• you can then scale to your desired range

Scaling to desired range

function getRandomInt(max) {
  return Math.floor(Math.random() * max);
}

console.log(getRandomInt(3));
// Expected output: 0, 1 or 2

Scale shifting to desired min range

function getRandomArbitrary(min, max) {
  return Math.random() * (max - min) + min;
}

Security Concerns

Math.random() does not provide cryptographically secure random numbers.

• Do not use them for anything related to security.

See crypto.