w3school of random () Tutorial
definition and usage
random () method returns a random number ranging between 0 and 1.
grammar
Math.random()
return value
A pseudo-random number between 0.0 and 1.0.
Examples
Take 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 to specify a range of values
Using parseInt (), Math.floor () or Math.ceil () rounded off
Directly Math.random () method, generated is a number less than 1,
Math.random()*5
The result is a random number less than 5. And we usually want to get is an integer between 0-5 result by rounding get integer.
parseInt (), the Math. Floor () and the Math. ceil () can play a role in rounding.
var randomNum = Math.random()*5;
alert(randomNum); // 2.9045290905811183
alert(parseInt(randomNum,10)); // 2
alert(Math.floor(randomNum)); // 2
alert(Math.ceil(randomNum)); // 3
Note: the parseInt () and . The Math Floor () effect is the same, are rounded down integer part .
Therefore, the parseInt (Math.random () * 5,10) and the Math .floor (Math.random () *. 5) are generated by a random number between 0-4 ,
the Math. Ceil (Math.random (). 5 * ) is generated by a random number between 1-5 .
Generating a random number value specified range
So, if you want to generate a random number to any value, the formula is this:
// max - a desired maximum value
the parseInt (Math.random () * max, 10) + 1'd ;
Math.floor(Math.random()*max)+1;
Math.ceil(Math.random()*max);
If generation 0 to any value of a random number:
// max - a desired maximum value
the parseInt (Math.random () * (+ max. 1), 10 );
Math.floor(Math.random()*(max+1));
If the generated arbitrary value to an arbitrary value of the random number:
// max - maximum desired
// min - minimum desired
the parseInt (Math.random () * (max-min +. 1) + min, 10 );
Math.floor(Math.random()*(max-min+1)+min);