Minimum allowed comment length only on a specific page

Question

This is the function I use to only allow comments longer than 60 chars:

add_filter( 'preprocess_comment', 'wpb_preprocess_comment' );
function wpb_preprocess_comment($comment) {
if ( strlen( $comment['comment_content'] ) < 60 ) {
    wp_die('Minimum allowed comment length is 60 characters.');
}
return $comment;
}

How do I make this filter apply to comments only on a specific page, say, is_page(42)?

Answer 1

is_page() is not available at that point try using global $post that way the post ID should be available for comparison.

add_filter( 'preprocess_comment', 'wpb_preprocess_comment' );
function wpb_preprocess_comment($comment) {
global $post;
if ((strlen( $comment['comment_content'] ) < 60 ) && ($post->ID == 42)) {
    wp_die('Minimum allowed comment length is 60 characters.');
}
return $comment;
}