在用户屏幕上显示html元素时执行ajax

I have this script which makes ajax request when user reaches the end of the page. It is based on scroll event. At page load I am showing only 16 products on the user screen and when he scrolls down I wish to load another 16 products. My script is working but it executes more than one ajax request which is not what I want. The idea is just to show another set of 16 products. The script is:I have this script which makes ajax request whe