# In javascript, how does random number math random generate a random number in a specified range? mathrandom

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In javascript, how does random number math random generate a random number in a specified range? mathrandom

Today, a friend asked me how to generate a random number in the specified range in JavaScript. Math. random () is used to generate random numbers. However, the general reference manual does not explain how to use this method to generate random numbers within a specified range. This time I will introduce Math. random () in detail and how to use it to generate random numbers within the specified range.

W3school's random () Tutorial

Definition and usage

The random () method returns a value ranging from 0 ~ A random number between 1.

Syntax

Math. random ()

Return Value

0.0 ~ A pseudo-random number between 1.0.

Instance

In this example, we will obtain a random number between 0 and 1:

`<Script type = "text/javascript"> document. write (Math. random (); </script> // output: 0.15246391076246546`

How to generate a random number with a specified range value

After reading the w3school tutorial, you should know the basic usage of the Math. random () method.

Rounding data using parseInt (), Math. floor (), or Math. ceil ()

We can see that the Math. random () method is used directly to generate a number smaller than 1, so:

Math. random () * 5

The result is a random number less than 5. What we usually want to get is an integer between 0 and 5, so we need to round the result to get the expected integer. ParseInt (), Math. floor (), and Math. ceil () can all play a rounding role.

`var randomNum = Math.random()*5;alert(randomNum); // 2.9045290905811183 alert(parseInt(randomNum,10)); // 2alert(Math.floor(randomNum)); // 2alert(Math.ceil(randomNum)); // 3`

From the test code, we can see that the effects of parseInt () and Math. floor () are the same, all of which are down integers. So parseInt (Math. random () * 5, 10) and Math. floor (Math. random () * 5) is a random number between 0 and 4, Math. ceil (Math. random () * 5) is a random number between 1 and 5.
Generate random numbers within a specified range

Therefore, if you want to generate a random number ranging from 1 to any value, the formula is as follows:

`// Max-the expected maximum value parseInt (Math. random () * max, 10) + 1; Math. floor (Math. random () * max) + 1; Math. ceil (Math. random () * max );`

If you want to generate a random number ranging from 0 to any value, the formula is as follows:

`// Max-the expected maximum value parseInt (Math. random () * (max + 1), 10); Math. floor (Math. random () * (max + 1); if you want to generate a random number from any value to any value, the formula is as follows: // max-the expected maximum value // min-the expected minimum value parseInt (Math. random () * (max-min + 1) + min, 10); Math. floor (Math. random () * (max-min + 1) + min );`

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