<!DOCTYPE html>
<style>
#popup{
position: fixed;
background: rgba(0, 0, 0, 0.8);
box-shadow: 0 0 5px black;
padding: 3px 6px;
color: white;
font: 12px Arial;
}
</style>
<a href="#">Ссыкла какая нибудь</a>
<div id="popup" style="display:none">дивчик</div>
<script>
(function(){
var link = document.querySelector('a');
var popup = document.getElementById('popup');
link.addEventListener('click', function(e){
e.preventDefault();
popup.style.display = 'block';
popup.style.left = e.pageX - popup.offsetWidth + 'px';
popup.style.top = e.pageY + 'px';
});
})();
</script>