javascript - how can i add class 2,5,8 etc number div -

i creating gallery, bellow sample html code

<div class="probox">          <img src="pro/th/chair.jpg" />           <h2>chair</h2>       </div>   <div class="probox">          <img src="pro/th/chair.jpg" />           <h2>chair</h2>       </div>   <div class="probox">          <img src="pro/th/chair.jpg" />           <h2>chair</h2>       </div>  <div class="probox">          <img src="pro/th/chair.jpg" />           <h2>chair</h2>       </div>   <div class="probox">          <img src="pro/th/chair.jpg" />           <h2>chair</h2>       </div>    <div class="probox">          <img src="pro/th/chair.jpg" />           <h2>chair</h2>       </div>    <div class="probox">          <img src="pro/th/chair.jpg" />           <h2>chair</h2>       </div>   <div class="probox">          <img src="pro/th/chair.jpg" />           <h2>chair</h2>       </div> 

ok in page show 3 thumbnail each row, want add class each row 2nd div. 1st row 2nd div 2nd row 2nd div... mean 2nd div next 5th div next 8th div etc way..

or if how can add class each 3rd div.. 3rd div, 6th div, 9th div etc..

http://jsfiddle.net/cyber007/wj5fd/

try,

$('.productsarea .probox:nth-child(3n)').addclass('yourclass'); 

demo