Table of contents (TOC) plugin is not showing header tag

I made a post template using meta box(custom field). If I put data into metabox, the template part (contents with h2, h3, p) shows up at the bottom of post (not on post edit page). However, every TOC plugins use revisions to check if there is h2 or h3 like this code.

public function widget( $args, $instance ) {
        global $ht_kb_toc_tools, $wp_query;

        if( ! is_singular() )
            return;

        if ( ! isset( $wp_query ) ) {
            return;
        }


        if( is_a($ht_kb_toc_tools, 'HT_KB_TOC_Tools') ){
            if( $ht_kb_toc_tools-ht_block_toc_detected  apply_filters('ht_kb_toc_disable_on_ht_block_toc', true ) ){
                //early exit if ht-block-toc detected
                return;    
            }                
        }

        extract( $args, EXTR_SKIP );

        $instance = wp_parse_args( $instance, $this-defaults );

        //$post = get_post( $wp_query-post-ID );
        $post = get_post();

        if( is_preview() ){
            //get the post revisions
            $post_revisions = ( wp_get_post_revisions( $post ) );

            if ( !empty( $post_revisions ) ) {
                //get the latest revision - this should be the current preview
                $post = current( $post_revisions );
            }
        }

        $title = apply_filters( 'widget_title', empty( $instance['title'] ) ? '' : $instance['title'], $instance, $this-id_base );   

        if(is_a($ht_kb_toc_tools, 'HT_KB_TOC_Tools')){

            //extract headings
            $headings = $ht_kb_toc_tools-ht_kb_toc_extract_headings( do_shortcode( $post-post_content ), true ); 

            //don't output widget if no headings are in content
            if(empty($headings))
                return;

            echo $before_widget;

            if ( $title )
                echo $before_title . $title . $after_title;


            ?
            nav id=navtoc role=navigation

                

            ?php
            //display items
            $ht_kb_toc_tools-ht_kb_display_items();
            ?

            /nav

            ?php
        }

        echo $after_widget;

    } // end widget

Is there another way to check h2 or h3 beside checking revision? or is there a way that shows my metabox data show on post edit page? Thanks.