No check for DOING_AJAX

While debugging an issue with another plugin, I noticed that this plugin outputs its html and css directly into ajax responses.

There is a filter() method in the plugin that ironically contains no filters at all.. and the plugin even has a method called doing_ajax() that isnt even used, anywhere!!

Please either use your own doing_ajax check, or at least provide a filter for other plugins to stop this behaviour.

For anyone else running into this issue simply adding the following to the top of your filter() method will fix the javascript errors.

if( WPFront_Static::doing_ajax() ) {
    return false;
}