Is it possible to include the add_filter() function within a shortcode function

Question

I am trying to pass content to the 'google_dfp_ad_slot' filter. Can this be done within a shortcode funcion?

/**
     * Shortcode function to dynamically add google dfp ads to inline content and widgets
     *
     * [fopconnect_ad is_page="true" page="about"]
     *   {JS}googletag.defineSlot('/6111408/FOPC_All_LeaderBoard_728x90', [728, 90], 'div-gpt-ad-1398288352265-0').addService(googletag.pubads());{/JS}
     *   {HTML}<div id='div-gpt-ad-1342652501811-0' style='width:160px; height:600px;'><script type='text/javascript'>googletag.cmd.push(function() { googletag.display('div-gpt-ad-1342652501811-0'); });</script></div>{/HTML}
     * [/fopconnect_ad]
     *
     * @param  array $atts    shortcode attributes
     * @param  string $content
     * @return sting
     */



    add_shortcode( 'fopconnect_ad', 'fopconnect_ad_func' );
    function fopconnect_ad_func( $atts, $content ) {
        extract( shortcode_atts( array(
            'is_page' => false,
            'page' => '' // can be title, slug, or id
        ), $atts ) );

        preg_match("#\\{JS\\}(.*?)\\{/JS\\}#s", $content, $matches);
        $js = ( !empty( $matches[1] ) ? $matches[1] : '' );

        preg_match("#\\{HTML\\}(.*?)\\{/HTML\\}#s", $content, $matches);
        $content = ( !empty( $matches[1] ) ? $matches[1] : '' );

        if ( $is_page && is_page( explode(', ', $page) ) ) {
            add_filter( 'google_dfp_ad_slot', function( $js ) { return $js; } );
        }

        if ( $is_page && is_page( explode(', ', $page) ) ) {
            return $content;
        }

    }

Answer 1

It should be possible but you will have to be aware of timing issues. Your shortcode will have to execute before whatever hook you are hooking into.

That is, you can't hook into wp_enqueue_scripts or wp_head but you should be able to hook into later hooks like wp_footer. I suspect that timing is the problem.