как-то так ...
<!doctype html>
<style>
div{
position:absolute;
left:-100px;
width:100px;
height:50px;
background:#ccc
}
</style>
<div class="js"></div>
<div class="js" style="top: 120px;"></div>
<script>
var elements = document.querySelectorAll('.js');
for (var i = 0, len = elements.length; i < len; ++i) {
var animation = elements[i].animate([{
left: '-100px'
}, {left: '0' }
], { fill: 'forwards' ,
duration: 3000,
iterations: 1,
direction: 'normal',
easing: 'linear',
delay: 0
});
}
</script>