Display thumbnail image when mouse hover #javascript

html + javascript

<span class="help-block"><a rel="featured_image_popover" href="<?=$data['post_featured_image'];?>" data-img="<?=$data['post_featured_image'];?>" target="_blank">image's URL</a></span>


$('a[rel=featured_image_popover]').popover({
    html: true,
    trigger: 'hover',
    placement: 'bottom',
    content: function () { return '<img class="img-responsive" src="' + $(this).data('img') + '" />'; }
});