Trigger event when user scroll to specific element - with jQuery

Question

I have an h1 that is far down a page..

<h1 id="scroll-to">TRIGGER EVENT WHEN SCROLLED TO.</h1>

and I want to trigger an alert when the user scrolls to the h1, or has it in it's browser's view.

$('#scroll-to').scroll(function() {
     alert('you have scrolled to the h1!');
});

how do I do this?

Answer 1

You can calculate the offset of the element and then compare that with the scroll value like:

$(window).scroll(function() {
   var hT = $('#scroll-to').offset().top,
       hH = $('#scroll-to').outerHeight(),
       wH = $(window).height(),
       wS = $(this).scrollTop();
   if (wS > (hT+hH-wH)){
       console.log('H1 on the view!');
   }
});

Check this Demo Fiddle

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Updated Demo Fiddle no alert -- instead FadeIn() the element

---

Updated code to check if the element is inside the viewport or not. Thus this works whether you are scrolling up or down adding some rules to the if statement:

   if (wS > (hT+hH-wH) && (hT > wS) && (wS+wH > hT+hH)){
       //Do something
   }

Demo Fiddle