WordPress performance stats

functions.php

<?php

// Register function if WordPress is in debug mode
if ( true == 'WP_DEBUG' ) {
  add_action( 'wp_footer', 'the_performance_stats' );
}

performance-stats.php

<?php

function get_performance_stats()
{
  $stats = '<script>';

  $stats .= 'console.info("Queries:", "' . get_num_queries() . '");';
  $stats .= 'console.info("Execution time:", "' . timer_stop() . 's");';
  $stats .= 'console.info("Memory usage:", "' . round( memory_get_usage() / 1024 / 1024, 2 ) . '", "MB");';

  if ( current_user_can( 'administrator' ) ) {
    global $wpdb;

    $stats .= 'console.group("DB queries");';

    foreach ( $wpdb->queries as $query ) {
      $stats .= 'console.group();';

      foreach ( $query as $query ) {
        $stats .= 'console.log("' . $query . '");';
      }

      $stats .= 'console.groupEnd();';
    }

    $stats .= 'console.groupEnd();';
  }

  $stats .= '</script>';

  return $stats;
}

function the_performance_stats()
{
  echo $this->get_performance_stats();
}