Math.random()
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.
Note: 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.
Syntax
Math.random()
Return value
A floating-point, pseudo-random number between 0
(inclusive) and 1
(exclusive).
Examples
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.
Getting a random number between 0 (inclusive) and 1 (exclusive)
function getRandom() {
return Math.random();
}
Getting a random number between two values
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;
}
Getting a random integer between two values
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
}
Note: 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.
Getting a random integer between two values, inclusive
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
}
Specifications
Specification |
---|
ECMAScript Language Specification # sec-math.random |
Browser compatibility
BCD tables only load in the browser