OK guys, me being impatient to wait for an answer found a solution, so I’m just gonna paste it here for anyone else running into something like this. It was simple really, I just didn’t realize since I rely too much on jQuery sometimes. Here:
var listing = document.querySelector('.card-' +postID);
listing.addEventListener('mouseover', function() {
infowindow.open( map, marker );
});
listing.addEventListener('mouseout', function() {
infowindow.close();
});