No need in timeout, use reflow to apply the change:
function reset_animation() {
var el = document.getElementById('animated');
el.style.animation = 'none';
el.offsetHeight; /* trigger reflow */
el.style.animation = null;
}
#animated {
position: absolute;
width: 50px; height: 50px;
background-color: black;
animation: bounce 3s ease-in-out infinite;
}
@keyframes bounce {
0% { left: 0; }
50% { left: calc( 100% - 50px ); }
100% { left: 0; }
}
<div id="animated"></div>
<button onclick="reset_animation()">Reset</button>