keep image inside viewport when animating with jquery code example

Example 1: jquery scroll when object appear on screen make animation

$(window).on("scroll", function(){
  if($(window).scrollTop() + $(window).height() - 100 >= $(".target").offset().top){
    alert("On viewport");
  }
})

Example 2: jquery scroll when object appear on screen make animation

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<div class="target">
</div>