The `Math.random()`

function returns a floating-point, pseudo-random number in the range 0 to less than 1 (inclusive of 0, but not 1) with approximately uniform distribution over that range — 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.

`Math.random()`

*does not* provide cryptographically secure random numbers. Do not use them for anything related to security. Use the Web Crypto API instead, and more precisely the `window.crypto.getRandomValues()`

method.

Math.random()

A floating-point, pseudo-random number between `0`

(inclusive) and 1 (exclusive).

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 (2^{53} or higher), it's possible in *extremely* rare cases to calculate the usually-excluded upper bound.

function getRandom() { return Math.random(); }

This example returns a random number between the specified values. The returned value is no lower than (and may possibly equal) `min`

, and is less than (and not equal) `max`

.

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

This example returns a random *integer* between the specified values. The value is no lower than `min`

(or the next integer greater than `min`

if `min`

isn't an integer), and is less than (but not equal to) `max`

.

function getRandomInt(min, max) { min = Math.ceil(min); max = Math.floor(max); return Math.floor(Math.random() * (max - min) + min); //The maximum is exclusive and the minimum is inclusive }

It might be tempting to use `Math.round()`

to accomplish that, but doing so would cause your random numbers to follow a non-uniform distribution, which may not be acceptable for your needs.

While the `getRandomInt()`

function above is inclusive at the minimum, it's exclusive at the maximum. What if you need the results to be inclusive at both the minimum and the maximum? The `getRandomIntInclusive()`

function below accomplishes that.

function getRandomIntInclusive(min, max) { min = Math.ceil(min); max = Math.floor(max); return Math.floor(Math.random() * (max - min + 1) + min); //The maximum is inclusive and the minimum is inclusive }

Desktop | ||||||
---|---|---|---|---|---|---|

`random` |
1 | 12 | 1 | 3 | 3 | 1 |

Mobile | ||||||
---|---|---|---|---|---|---|

`random` |
1 | 18 | 4 | 10.1 | 1 | 1.0 |

Server | |
---|---|

`random` |
0.1.100 |

© 2005–2018 Mozilla Developer Network and individual contributors.

Licensed under the Creative Commons Attribution-ShareAlike License v2.5 or later.

https://wiki.developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Math/random