Javascript Function with Class

Good,

I have the following code that runs a sequence of images:

 var setInter = null
 function startAnimation() {
     var frames = document.getElementById("animation").children;
     var frameCount = frames.length;
     var i = 0;
     setInter = setInterval(function () {
         frames[i % frameCount].style.display = "none";
         frames[++i % frameCount].style.display = "block";
         if(i>=18){ 
             clearInterval(setInter);
         }
     }, 100);
 }

This runs an animation by frames, and when the condition happens, ie 19 frames, the animation stops.

I want the animation to happen when the #animation div has the class "in-view". This part is already treated, and when I scroll to the div, it gains the class "in-view", however I do not arrange the form of the activate function and the animation happens.

Solutions other than JQuery.

Thank you!