JavaScript Random

Math.random()

Math.random() returns a random number between 0 (inclusive),  and 1 (exclusive):

Example

Math.random();              // returns a random number

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Math.random() always returns a number lower than 1.


JavaScript Random Integers

Math.random() used with Math.floor() can be used to return random integers.

Example

Math.floor(Math.random() * 10);     // returns a random integer from 0 to 9

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Example

Math.floor(Math.random() * 11);      // returns a random integer from 0 to 10

Example

Math.floor(Math.random() * 100);     // returns a random integer from 0 to 99

Example

Math.floor(Math.random() * 101);     // returns a random integer from 0 to 100

Example

Math.floor(Math.random() * 10) + 1;  // returns a random integer from 1 to 10

Example

Math.floor(Math.random() * 100) + 1; // returns a random integer from 1 to 100

A Proper Random Function

As you can see from the examples above, it might be a good idea to create a proper random function to use for all random integer purposes.

This JavaScript function always returns a random number between min (included) and max (excluded):

Example

function getRndInteger(min, max) {
return Math.floor(Math.random() * (max – min) ) + min;
}

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This JavaScript function always returns a random number between min and max (both included):

Example

function getRndInteger(min, max) {
return Math.floor(Math.random() * (max – min + 1) ) + min;
}