defer-wordpress-scripts.php

<?php 

/*
| --------------------------------------------------------------------------
| DEFER on scripts
| function to add async and defer attributes
| --------------------------------------------------------------------------
*/

function defer_js_async($tag){

  ## 1: list of scripts ( by file name)  to defer.
  $scripts_to_defer = array(
    'owl-carousel.min.js',
    'mansonry.js',
    'imgloaded.js',
    'jquery.magnific-popup.min.js',
    'bgswitcher.js',
    'exit.js',
    'lazyload.js',
    'app.js',
    'cookie.js',
    'autocomplete',

    // WooCommerce
    'add-to-cart.min.js',
    'cart-fragments.min.js',
    'jquery.cookie.min.js',
    'jquery.blockUI.min.js',
    'woocommerce.min.js',
    'single-product.min.js',

    // Wordpress

    'wp-embed.min.js'
  );

  
  // If we want to defer scripts only on some pages ( here jQuery only on the home page )
  if( is_front_page() ) $scripts_to_defer[] = "jquery.js";


  #defer scripts we add the defer attribute to the scripts 
  foreach($scripts_to_defer as $defer_script){

    if(strpos($tag, $defer_script ) ){

      return str_replace( ' src', ' defer="defer" src', $tag );

    } 
  
  }

  return $tag;
}

if(!is_admin() && !is_user_logged_in()) {

  add_filter( 'script_loader_tag', 'defer_js_async', 10 );

}

remove-css-on-specific-pages.php

<?php 

/*
| --------------------------------------------------------------------------
| CSS management 
| Remove some CSS files from specific pages : front-page / product page / category / offline
| --------------------------------------------------------------------------
*/

add_filter( 'style_loader_tag', function($tag){

  // list of CSS to remove 
  $cssToRemove = array();

  
   // condition : which pages 
  if( 
    is_front_page() 
    || is_product() 
    || is_product_category()
    || is_page_template( 'template-offline.php') 
  ){
     
    // We push in the array a list of CSS files to remove 
    array_push($cssToRemove,
      "woocommerce.css",
      "woocommerce-smallscreen.css",
      "woocommerce-layout.css",
      "titan-framework-flux-settings-css"
    );

  } 


   // For each Style we check if it must be excluded
  foreach($cssToRemove as $css){

    if(strpos($tag, $css ) ) return false;

  }

  return $tag;

}, 10 );