JS Math.random () generates a random number for a specified range of values

The Math.random function does not produce an exponential range of data like the RAND function of PHP, and math.random only generates a pseudo-random number, which is then processed by us.today there is another netizen asked me how JavaScript generates a specified range of numeric 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 a random number within a set range.

W3school's random () tutorial
Definition and usage

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

Math.random ()

return value

A pseudo-random number between 0.0 ~ 1.0.
Instance

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

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<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 W3school's tutorial, you should know the basic usage of the Math.random () method.
Rounding processing with parseint (), Math.floor (), or Math.ceil ()

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

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Math.random ()

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

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var randomnum = Math.random (); alert (randomnum); 2.9045290905811183 Alert (parseint (randomnum,10)); 2 Alert (Math.floor (Randomnum)); 2 Alert (Math.ceil (Randomnum)); 3

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

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

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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 from 0 to any value, this is the formula:

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

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

Max-Desired Maximum value
Min-Desired Minimum value
parseint (Math.random () * (max-min+1) +min,10);
Math.floor (Math.random () * (max-min+1) +min);

Reference:

Http://www.111cn.net/wy/js-ajax/57062.htm

JS Math.random () generates a random number for a specified range of values