fade in div when user scrolls down page?

Question

I am trying to get a div to fade in using javascript when a user scolls down the page, the problem i am having is although it fades in it is fading in and fading out multiple times very quickly like its pulsating.

i only want it so that the div fades in slowly once when the user scrolls down the page. can someone please help?

<script>
   $(window).scroll(function(){
       var leftToBottom = $(document).height() - $(window).height() - $(window).scrollTop();
       var distanceFromTop = $(window).scrollTop();
       if( distanceFromTop > 600 && !$("profile_intro_case5").is(":visible") 
          && leftToBottom > 600) {
            $(".profile_intro_case5").fadeIn();
       }else if($(".profile_intro_case5").is(":visible") && (distanceFromTop < 600 || leftToBottom < 600)){
            $(".profile_intro_case5").fadeOut();
      }
   });
</script>

Answer 1

Check that the element is not currently being animated: !$(".profile_intro_case5").is(":animated")

   $(window).scroll(function(){
       var leftToBottom = $(document).height() - $(window).height() - $(window).scrollTop();
       var distanceFromTop = $(window).scrollTop();
       if( distanceFromTop > 600 && !$("profile_intro_case5").is(":visible") 
          && leftToBottom > 600 && !$(".profile_intro_case5").is(":animated")) {
                $(".profile_intro_case5").fadeIn();
       }else if($(".profile_intro_case5").is(":visible") && (distanceFromTop < 600 || leftToBottom < 600) && !$(".profile_intro_case5").is(":animated")){
                $(".profile_intro_case5").fadeOut();
      }
   });