I am using a javascript that's called 'Backstretch' to display an image on the back of my website that resizes when the viewport is getting bigger or smaller. Now I would like to combine it with the get_post_thumbnail function from WordPress so I can set a background image as featured image.
I tried the standard WP function but that doesn't work because it adds tags:
$.backstretch("<?php echo get_the_post_thumbnail( $post_id, $size, $attr ); ?>");
So I need to strip off those tags.. I'm getting close because i'm now getting an url (and image) but it's always the same one even though I set a different featured image on every page
<?php $url = wp_get_attachment_url( get_post_thumbnail_id($post_id, $size, $attr ) ); ?>
<script>$.backstretch("<?php echo $url; ?>");</script>