# Random number in JavaScript math random how to generate a random number of values for a specified range _javascript tips

Source: Internet
Author: User

Today, a friend asked me: How JavaScript generates a specified range of numerical random numbers. Math.random () This method is believed to be known to generate random numbers. However, the general reference manual does not show how to use this method to generate random numbers within a specified range. This time I'll give you a detailed introduction to Math.random () and how to use it to generate random numbers within the scope of the development.

W3school's random () tutorial

Definitions and usage

The random () method can return a random number between 0 ~ 1.

Grammar

Math.random ()

return value

A pseudo random number between 0.0 ~ 1.0.

Instance

In this case, we'll get 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 for a specified range value

After reading the W3school tutorial, you should know the basic usage of the Math.random () method.

Rounding with parseint (), Math.floor () or Math.ceil ()

We see that the direct use of the Math.random () method produces a number less than 1, so:

Math.random () *5

The result is a random number less than 5. And what we usually want is an integer between 0-5, so we need to round up the resulting results and get the integers we expect. parseint (), Math.floor () and Math.ceil () can all be rounded up.

```var randomnum = Math.random () *5;

As we can see from the test code, the effect of the parseint () and Math.floor () is the same, and all the parts of the integer are taken down. So parseint (Math.random () *5,10) and Math.floor (Math.random () *5) are random numbers between 0-4 generated, Math.ceil (Math.random () *5) is the number of random numbers between 1-5 generated.
Generate a specified range of numeric random numbers

So, if you want to generate random numbers of 1 to any value, the formula is this:

```Max-Desired Maximum value
parseint (Math.random () *max,10) +1;
Math.floor (Math.random () *max) +1;
Math.ceil (Math.random () *max);```

If you want to generate random numbers of 0 to any value, the formula is this:

```Max-expected maximum value
parseint (Math.random () * (max+1), ten);
Math.floor (Math.random () * (max+1));
If you want to generate random numbers of arbitrary values to any value, the formula is this:
//MAX-expected maximum
/min-Expected minimum value
parseint (Math.random () * (max-min+1) +min,10);
Math.floor (Math.random () * (max-min+1) +min);```

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