I have a function that fires every time a slide is advanced in my slideshow, and increments a counter.

I want a simple way to call a function every X slide (5 in the example code). I realize I can do this easily using modulus but the syntax escapes me.

 var numSlides = $('.item').length; // 20
 var currSlide = 0;
 var ad_interval = 5;

 function updateSlide (){ 
    currSlide++
    // if we are at the ad interval, every 5 slides, call the next line
     $("#adslot").reveal();

 }

I have a function that fires every time a slide is advanced in my slideshow, and increments a counter.

I want a simple way to call a function every X slide (5 in the example code). I realize I can do this easily using modulus but the syntax escapes me.

 var numSlides = $('.item').length; // 20
 var currSlide = 0;
 var ad_interval = 5;

 function updateSlide (){ 
    currSlide++
    // if we are at the ad interval, every 5 slides, call the next line
     $("#adslot").reveal();

 }

• javascript
• jquery
• counter
• modulus

5 Answers 5

Mod returns the remainder... When it's 0, you've hit a count on the interval.

if((currSlide % ad_interval) === 0) {
   $('#adslot').reveal();
}

if (currSlide % ad_interval === 0) {
    // Note that this will also include the first (0th) slide.
}

Inside your updateSlide() method, you can include something like :

if(currSlide % ad_interval === 0)
{
     // Run method code.
}

This will run a method every 5 slides. For more information on Java operators and the modulus operator, this site does a pretty good job of explaining them.

Re you looking for this?

if (currSlide%5 ==0) {
  $("#adslot").reveal();
 }

I'd suggest:

function updateSlide (){
    // if we are at the ad interval, every 5 slides, call the next line
    if ((currSlide + 1) % ad_interval == 0){
        $("#adslot").reveal();
    }
    currslide++;
}

The reason I'm using (currSlide + 1) % ad_interval is simply because your index is zero-based, and the fifth slide would be at index 4, rather than 5; the +1 simply ensures that the the modulus will be 0 at the fifth slide, rather than the sixth.

This will also prevent the first, zeroth, slide from showing the ad.