With the WordPress plugin IncludeMe I've included a PHP script with PHP, HTML and Javascript on a wordPress page.

The script tries to get information from a second script, which is producing Json, using the async-fetch functionality of Javascript in the first script.

This is working well if using the HTML-tag iframe on the WordPress page. But not with the IncludeMe or other plugins I've tried: in that case WordPress is blocking async.

Also with the WordPress plugin 'Async Javascript' the blocking still happens. (In Async Javascript I've added my scripts under 'Scripts to Async')

Is 'Async Javascript' the way to get Javascript async under WordPress working? Or is there another/better way?