Peepso: Add extra data field (custom post meta) to postbox

I’am looking for the exact same thing, but haven’t found the solution yet.

Beware: the below code is from the legacy version from 2015…

There is a event when an activity is saved (see full code here):

    /**
     * Called on post save
     * @param {object} json JSON object
     */
    this.on_save = function(json) {
        if (typeof(Function) === typeof(this.opts.on_save))
            this.opts.on_save.apply(this, [json]);

        jQuery(this).trigger("postbox.post_saved", this);
    };

But I don’t know how to get the data in the response. I can fetch the event like this:

$( document ).on( 'postbox.post_saved', ( e ) => {
    console.log( e );
});

But the JSON-Object from the on_save-function above is missing. Otherwise we could resend another ajax-call and save the extra fields on our own.