W3Schools Tryit Editor

<!DOCTYPE html>
<html>
<head>
<style> 
div {
  width: 100px;
  height: 100px;
  background: red;
  position: relative;
  animation: mymove 5s 1;
}

@keyframes mymove {
  from {left: 0px;}
  to {left: 200px;}
}
</style>
</head>
<body>

<h1>Change animation-iteration-count with JavaScript</h1>

<p>Click the "Try it" button to make animation play forever!</p>
<button onclick="myFunction()">Try it</button>
<div id="myDIV"></div>

<p><strong>Note:</strong> Click the button BEFORE the animation is finished! Else it will not have any affect because the animation will not start over once it has finished.</p>
<p><strong>Note:</strong> The animationIterationCount property is not supported in Internet Explorer 11 or earlier versions.</p>

</body>

</html>