JAVASCRIPT

if user logged in wordpress

if ( is_user_logged_in() ) {
   // your code for logged in user 
} else {
   // your code for logged out user 
}

how to check if user is logged in wordpress

<?php 
if ( is_user_logged_in() ) {
  echo 'Welcome, logged in user. <a href="'.wp_logout_url().'">Click here to logout</a>.';
}else{
  echo 'Please login by <a href="'.wp_login_url().'">clicking here</a>.'
}

detect logged user wordpress javascript

document.body.classList.contains( 'logged-in' );