React to AJAX adding to the page

Found this at https://codex.wordpress.org/AJAX_in_Plugins

JavaScript triggering the post-load event after content has been inserted via Ajax:
jQuery( document.body ).trigger( 'post-load' );

JavaScript listening to the post-load event:

jQuery( document.body ).on( 'post-load', function () {
// New content has been added to the page. } );

I suppose it’s up to each plugin to trigger whichever event it wants when it’s done or none at all.