Math.random()

The Math.random() function returns a floating-point, pseudo-random number in the range [0, 1) that is, from 0 (inclusive) up to but not including 1 (exclusive), which you can then scale to your desired range. The implementation selects the initial seed to the random number generation algorithm; it cannot be chosen or reset by the user.

Syntax

Math.random()

Return value

A floating-point, pseudo-random number between 0 (inclusive) and 1 (exclusive).

Examples

Using Math.random()

Note that as numbers in JavaScript are IEEE 754 floating point numbers with round-to-nearest-even behavior, the ranges claimed for the functions below (excluding the one for Math.random() itself) aren't exact. If extremely large bounds are chosen (2⁵³ or higher), it's possible in extremely rare cases to calculate the usually-excluded upper bound.

// Returns a random number between 0 (inclusive) and 1 (exclusive)
function getRandom() {
  return Math.random();
}

// Returns a random number between min (inclusive) and max (exclusive)
function getRandomArbitrary(min, max) {
  return Math.random() * (max - min) + min;
}

// Returns a random integer between min (included) and max (excluded)
// Using Math.round() will give you a non-uniform distribution!
function getRandomInt(min, max) {
  min = Math.ceil(min);
  max = Math.floor(max);
  return Math.floor(Math.random() * (max - min)) + min;
}

// Returns a random integer between min (included) and max (included)
// Using Math.round() will give you a non-uniform distribution!
function getRandomIntInclusive(min, max) {
  min = Math.ceil(min);
  max = Math.floor(max);
  return Math.floor(Math.random() * (max - min + 1)) + min;
}

Specifications

Browser compatibility