JavaScript Random

// Returns a random number:

always returns a number lower than 1.

Math.random() used with Math.floor()

There is no such thing as JavaScript integers. We are talking about numbers with no decimals here.

// Return a random integer from 0 to 9 (both included):

Example outputs: 0.0, 0.237, 0.9999, but never 1.

Example possible results: 0.0, 3.5, 9.99, etc. Math.floor() rounds a number down to the nearest whole integer: 3.5 becomes 3 9.99 becomes 9 0.1 becomes 0

0 through 9 (both inclusive). In other words, the range is [0, 9].

// Return a random integer from 0 to 10 (both included):

// Return a random integer from 0 to 99 (both included):

// Return a random integer from 0 to 100 (both included):

// Return a random integer between 1 and 10 (both included):

Math.random() returns a number from 0 (inclusive) up to but not including 1. Multiplying by 10 gives a number from 0 up to but not including 10. Adding 1 shifts that range to 1 up to but not including 11. Math.floor() then rounds down, so you get an integer between 1 and 10.

// Returns a random integer from 1 to 100 (both included):

Math.random()

<1

<10

<100

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 integer between min (included) and max (excluded):