Using WordPress ‘core_upgrade_preamble()’ PHP function
Display upgrade WordPress for downloading latest or upgrading automatically form.
JavaScript
Using WordPress ‘get_parent_theme_file_uri()’ PHP function
Retrieves the URL of a file in the parent theme.
Using WordPress ‘js_escape()’ PHP function
Escape single quotes, specialchar double quotes, and fix line endings.
Using WordPress ‘get_user_count()’ PHP function
Returns the number of active users in your installation.