How do I defer or async this WordPress javascript snippet to load lastly for faster page load times?

Question

I have various javascripts that are necessary plugins in one of my WordPress domains, and I know where in the php file it\'s called from.

I\'m taking every measure I

Answer 1

To gain control over which js files to defer and avoid conflicts you can append a variable to the url in the wp_register_script function like below.

wp_register_script( 'menu', get_template_directory_uri() . '/js/script.js?defer', array('jquery'), '1.0', true );

Then change the line:

if ( FALSE === strpos( $url, '.js' ))

To:

if ( FALSE === strpos( $url, '.js?defer' ))

The new filter looks like this.

add_filter( 'clean_url', function( $url )
{
    if ( FALSE === strpos( $url, '.js?defer' ) )
    { // not our file
    return $url;
    }
    // Must be a ', not "!
    return "$url' defer='defer";
}, 11, 1 );

Answer 2

Or more universal way:

function add_async_forscript($url)
{
    if (strpos($url, '#asyncload')===false)
        return $url;
    else if (is_admin())
        return str_replace('#asyncload', '', $url);
    else
        return str_replace('#asyncload', '', $url)."' async='async"; 
}
add_filter('clean_url', 'add_async_forscript', 11, 1);

so you can add async to any script without code changes, just add #asyncload to script url as:

wp_enqueue_script('dcsnt', '/js/jquery.social.media.tabs.1.7.1.min.js#asyncload' )

Answer 3

Another solution using a different filter, which can be used to target a specific script handle:

function frontend_scripts()
{
    wp_enqueue_script( 'my-unique-script-handle', 'path/to/my/script.js' );
}
add_action( 'wp_enqueue_scripts', 'frontend_script' );

function make_script_async( $tag, $handle, $src )
{
    if ( 'my-unique-script-handle' != $handle ) {
        return $tag;
    }

    return str_replace( '<script', '<script async', $tag );
}
add_filter( 'script_loader_tag', 'make_script_async', 10, 3 );

Answer 4

Something to add the clean_url filter solution, make sure to validate to use it only on the font-end maybe using if( ! is_admin() ){} popular plugins like ACF might give you a headache.

Update

Here is my modified version of the solution:

if( ! is_admin() ){
  add_filter( 'clean_url', 'so_18944027_front_end_defer', 11, 1 );
  function so_18944027_front_end_defer( $url ) {
    if ( FALSE === strpos( $url, '.js' ) )
    { // not our file
        return $url;
    }
    // Must be a ', not "!
    return "$url' defer='defer";
  }
}

Answer 5

Incorporate the async attribute to the scripts so that they are only loaded once the whole page is loaded

<script type="text/javascript">
    function ngfbJavascript( d, s, id, url ) {
        var js, ngfb_js = d.getElementsByTagName( s )[0];
        if ( d.getElementById( id ) ) return;
        js = d.createElement( s );
        js.id = id;
        js.async = true;
        js.src = url;
        ngfb_js.parentNode.insertBefore( js, ngfb_js );
    };
</script>

Source:Here

Answer 6

A simplified method. Add to your functions.php file to make make JavaScript asynchronous in Wordpress

// Make JavaScript Asynchronous in Wordpress
add_filter( 'script_loader_tag', function ( $tag, $handle ) {    
    if( is_admin() ) {
        return $tag;
    }
    return str_replace( ' src', ' async src', $tag );
}, 10, 2 );