// Retrieve the ID of the current item in the WordPress Loop.
get_the_ID()
function get_the_ID() { // phpcs:ignore WordPress.NamingConventions.ValidFunctionName.FunctionNameInvalid
$post = get_post();
return ! empty( $post ) ? $post->ID : false;
}
$post = get_post( 123 ); // Where 123 is the ID
$output = apply_filters( 'the_content', $post->post_content );
url_to_postid( site_url('the_slug') );
get_posts(array(
'fields' => 'ids', // Only get post IDs
'posts_per_page' => -1
));