functions.php

<?php 

class Settings_Admin { 
  public function __construct() { 
     add_action( 'wp_head', array($this, 'add_script_to_fe') ); 
    add_action( 'admin_enqueue_scripts', array($this, 'add_custom_style_script') ); 
    add_filter( 'script_loader_tag', array($this,'defer_js'), 10,2 ); 
  }
 public function add_custom_style_script(){
   wp_register_style('wa_email_marketing', PLUGIN_URL . '/dist/css/main.css');
   wp_enqueue_style('wa_email_marketing');
  wp_register_script('wa_email_marketing', PLUGIN_URL . '/dist/js/root.js')
 } 
 public function defer_js($tag, $handle){
  $scripts_to_defer = array('wa_email_marketing'); 
  foreach($scripts_to_defer as $defer_script) {
    if ($defer_script === $handle) {
   return str_replace(' src', ' defer src', $tag);
  }
 }
 return $tag;
}
public function add_script_to_fe(){
  $script = 'var apiObject = "' . wp_json_encode(
   array(
    'homeUrl' => home_url(),
    'rootapiurl' => rest_url(),
    'nonce' => wp_create_nonce('wp_rest'),
    'plugin_url' => PLUGIN_URL,
    'user_id' => get_current_user_id(),
    )) . '";';
   if ( ! empty( $data ) ) {
   $script = "$data\n$script";
   }
  _e("\n<script type=\"text/javascript\">\n $script \n</script>\n",'_themename');
 }
}
?>