No need for functions and filters all you need to do is to use get_adjacent_post
instead of next_post_link
and prev_post_link
, Note that get_adjacent_post
is used to get previous and next post, you can read about it here
To get previous post and it's title attribute use this
$prev_post = get_adjacent_post(false, '', true);
if(!empty($prev_post)) {
echo '' . $prev_post->post_title . ''; }
To get next post and it's title attribute use this
$next_post = get_adjacent_post(false, '', false);
if(!empty($next_post)) {
echo '' . $next_post->post_title . ''; }