A positive number to a negative number in JavaScript?

Question

In principle, the reverse side of abs. If I have:

if($this.find('.pdxslide-activeSlide').index() < slideNum-1){ slideNum = -slideNum } console.log(slideNum) 

No matter which console ALWAYS returns a positive number. How to fix it?

If I do this:

 if($this.find('.pdxslide-activeSlide').index() < slideNum-1){ _selector.animate({left:(-slideNum*sizes.images.width)+'px'},750,'InOutPDX') } else{ _selector.animate({left:(slideNum*sizes.images.width)+'px'},750,'InOutPDX') } 

it works, but it’s NOT “DRY” and just stupid to have the whole block of JUST code for -

Answer 1

 Math.abs(num) => Always positive -Math.abs(num) => Always negative 

Do you really understand that for your code

 if($this.find('.pdxslide-activeSlide').index() < slideNum-1){ slideNum = -slideNum } console.log(slideNum) 

If the found index is 3 and slideNum is 3,
then 3 <3-1 => false
therefore slideNum remains positive

This is more like a logical mistake for me.

Answer 2

The reverse of abs is Math.abs(num) * -1 .

Answer 3

The basic formula for a positive negative or negative attitude towards a positive:

 i - (i * 2) 

Answer 4

Are you sure the control is in the if body? As with the condition in if ? Because if this is not the case, the if body will never be executed, and slideNum will remain positive. I'm going to fear that this is probably what you see.

If I try the following in Firebug, it works:

 >>> i = 5; console.log(i); i = -i; console.log(i); 5 -5 

slideNum *= -1 should also work. Like Math.abs(slideNum) * -1 .

Answer 5

To get the negative version of a number in JavaScript, you can always use the bitwise ~ operator.

For example, if you have a = 1000 , and you need to convert it to negative, you can do the following:

a = ~a + 1;

which will cause a to be -1000.

Answer 6

If you don't like using Math.Abs ​​* -1, you can make this simple statement if: P

 if (x > 0) { x = -x; } 

Of course you could make this function like this

 function makeNegative(number) { if (number > 0) { number = -number; } } 

makeNegative (-3) => -3 makeNegative (5) => -5

Hope this helps! Math.abs will probably work for you, but if it's not so little

Answer 7

Use 0 - x

x is the number you want to invert