Add class to custom thumbnail

Question

To generate a thumbnail for certain part of my theme i'm using the following code :

if(has_post_thumbnail() && !post_password_required() && !is_attachment() &&  wp_get_attachment_image_src(get_post_thumbnail_id(get_the_ID()))):
    $thumbnail_url = wp_get_attachment_image_src(get_post_thumbnail_id(get_the_ID()));
    $thumbnail = get_the_post_thumbnail(get_the_ID() );
else:
    $thumbnail_url[0] = get_template_directory_uri(). '/assets/images/no-image.jpg';
    $thumbnail = '<img src="'.esc_url(get_template_directory_uri(). '/assets/images/no-image.jpg').'" alt="'.get_the_title().'" />';
endif;
echo '<div class="post-thumbnail">'.$thumbnail.'</div>';

I would like to be able to add a class and an id from the post it's attached to to my code on this line $thumbnail = get_the_post_thumbnail(get_the_ID() ); but I can't figure out how to modify the code accordingly.

I want to be able to add some lightbox options to my thumbnails.

Answer 1

The third parameter you can pass to get_the_post_thumbnail is $attributes, which you can use to pass custom HTML attributes including classes.

$thumbnail = get_the_post_thumbnail(
    get_the_ID(), // Post ID.
    'thumbnail', // Image size.
    array( // Attributes
        'class' => 'my-custom class-names', // Classes go here.
    )
);

Note that this will override the default image classes that WordPress assigns (which is attachment-$size_class size-$size_class)