Code syntax error, “userfullName undefined”

You are missing the ‘echo’

userfullName = <?php $current_user->display_name;?>

should be

var userfullName = "<?php echo $current_user->display_name;?>"

AND notice that I put quotes around that too.

BUT!!!!

You should really look at using wp_localize_script for declaring javascript variables.

Example:

add_action('wp_enqueue_scripts', 'fobu_front_scripts');

function fobu_front_scripts() {

    global $blog_id;
    $params = array( 
        'site_url' => site_url(),
        'blog_id' => $blog_id
    );

    wp_localize_script( 'jquery', 'MyScriptParams', $params );
}