Generate a random number or integer in a range with JavaScript

JavaScript's Math.random() is handy for generating random numbers between 0 and 1. If you need a random number in a different range, you'll need to use some simple math to map the random number to the desired range.

Random number in a range

The simplest use case you'll come across is to generate a random number in a specified range. All you need to do is multiply the result of Math.random() by the difference between the maximum and minimum values, and then add the minimum value.

const randomNumberInRange = (min, max) => Math.random() * (max - min) + min;

randomNumberInRange(2, 10); // 6.0211363285087005

Random integer in a range

Subsequently, generating a random integer is very similar, except for an additional step at the end. You need to use Math.floor() to round the result down to the nearest integer.

const randomIntegerInRange = (min, max) =>
  Math.floor(Math.random() * (max - min + 1)) + min;

randomIntegerInRange(0, 5); // 2

Gaussian random numbers

Finally, if you need to generate Gaussian (normally distributed) random numbers, you can use the Box-Muller transform to generate random numbers with a Gaussian distribution.

const randomGauss = () => {
  const theta = 2 * Math.PI * Math.random();
  const rho = Math.sqrt(-2 * Math.log(1 - Math.random()));
  return (rho * Math.cos(theta)) / 10.0 + 0.5;
};

randomGauss(); // 0.5