This is generally useful in speed optimisations and can help a lot to reduce load time of pages specially when your site depend heavily on javascripts.

/*Defer parsing js*/
if ( ! is_admin() ) {
function defer_parsing_of_js ( $url ) {
    if ( FALSE === strpos( $url, '.js' ) ) return $url;
    if ( strpos( $url, 'jquery.js' ) ) return $url;
    return "$url' defer='defer";
}
add_filter( 'clean_url', 'defer_parsing_of_js', 11, 1 );
}
/*End Defer parsing js*/