Explain Math.floor(Math.random())

Question

I have seen many places using Math.floor() and Math.random()

like below

$(\'a.random-color\').hover(function() { //mouseove         


        

Answer 1

~~Number is only the Math.floor() for positive numbers. For negative numbers, it is the Math.ceil().

For positive numbers you can use:

Math.floor(x) == ~~(x)

Math.round(x) == ~~(x + 0.5)

Math.ceil(x) == ~~(x + 1)

For negative numbers you can use:

Math.ceil(x) == ~~(x)

Math.round(x) == ~~(x - 0.5)

Math.floor(x) == ~~(x - 1)

Answer 2

Math.random will give you a floating point number between 0 (inclusive) and 1 (exclusive).

Multiplying that by 256 will give you a number in the range 0 (inclusive) through 256 (exclusive), but still floating point.

Taking the floor of that number will give you an integer between 0 and 255 (both inclusive).

It's the integer from 0 to 255 that you need to construct RGB values like rgb(72,25,183).

Answer 3

It seems a random color is desired - one with each component random between 0 and 255.

Math.random() returns a random number on [0,1) (ie it may be exactly zero or up to but not including one).

Multiplying that random value by 256 gives a random number on the range [0,256) (ie it may be 255.99, but never 256). Almost there, but not quite.

Math.floor() rounds the number downwards to the nearest whole integer, making the result an integer on [0,255] as desired.

Answer 4

Math.random returns value between 0 and 1. You are multiplying it with 256 so it will return some float value between 0 and 256. math.floor will omit fraction value from it.

Answer 5

Math.floor will give a whole number and gets rid of the decimals.

Math.random returns a number between 0 and 1 and therefore will produce decimal numbers when multiplied with 256. Thats why you want to use floor to get rid of the decimals otherwise the rgb values won't work.

Answer 6

The Math.floor() is to drop the decimal portion of the Number. It is the opposite of Math.ceil().

You can also double the invert bitwise operator (~~) to achieve the same as Math.floor() (though of course the floor() method is much more readable to most).

~~(Math.random() * 256)