Get post id outside loop : Notice: Trying to get property of non-object

I am trying to get the post id outside the loop in functions.php.but what error i am getting : Notice: Trying to get property of non-object in functions.php on line 549

function theme_myeffecto_disable() {
  global $wp_query;
  $post_id = $wp_query->post->ID;

  $showreaction = get_post_meta( $post_id, 'post_reaction_show', true );
  $showreaction = isset($showreaction) ? $showreaction : true;
  var_dump($showreaction);
}
add_action( 'init', 'theme_myeffecto_disable', 20 );

and $showrating always comes false weather it is true or false 🙁