Wordpress - Trigger Javascript on Gutenberg (Block Editor) Save

Not sure if there is a better way, but I am listening to subscribe rather than adding an event listener to the button:

wp.data.subscribe(function () {
  var isSavingPost = wp.data.select('core/editor').isSavingPost();
  var isAutosavingPost = wp.data.select('core/editor').isAutosavingPost();

  if (isSavingPost && !isAutosavingPost) {
    // Here goes your AJAX code ......

  }
})

Official docs of the Post Editor data: https://wordpress.org/gutenberg/handbook/designers-developers/developers/data/data-core-editor/

Okay, so way way more hacky solution than I wanted, but got it working...

Here is a slightly simplified and abstracted way of doing it from my code, in case anyone ever needs to do the same (as I'm sure more plugins will in the near future.)

    var reload_check = false; var publish_button_click = false;
    jQuery(document).ready(function($) {
        add_publish_button_click = setInterval(function() {
            $publish_button = jQuery('.edit-post-header__settings .editor-post-publish-button');
            if ($publish_button && !publish_button_click) {
                publish_button_click = true;
                $publish_button.on('click', function() {
                    var reloader = setInterval(function() {
                        if (reload_check) {return;} else {reload_check = true;}
                        postsaving = wp.data.select('core/editor').isSavingPost();
                        autosaving = wp.data.select('core/editor').isAutosavingPost();
                        success = wp.data.select('core/editor').didPostSaveRequestSucceed();
                        console.log('Saving: '+postsaving+' - Autosaving: '+autosaving+' - Success: '+success);
                        if (postsaving || autosaving || !success) {classic_reload_check = false; return;}
                        clearInterval(reloader);

                        value = document.getElementById('metabox_input_id').value;
                        if (value == 'trigger_value') {
                            if (confirm('Page reload required. Refresh the page now?')) {
                                window.location.href = window.location.href+'&refreshed=1';
                            }
                        }
                    }, 1000);
                });
            }
        }, 500);
    });

...just need to change metabox_input_id and trigger_value to match as needed. :-)