I think the way I'm going to deal with this is to modify the widget to have an extra configurable property that will be used in the naming of the cookie that is used to decide to show the splash screen again or not. The property will get updated by the administrator anytime that they add updated "what's new" information to the splash screen (or a new link to a separate blog post about the update), the property must be unique so will arbitrarily contain the date the update was made.
It will cause cookies to build up on the users pc, but I'm not too worried about hitting the max cookies or max cookies per domain.
I've got the main widget working, now I need to get the extra parameter added to the configuration page so it can be updated in the WAB instead of just directly in the json.
_getCookieKey: function() {
return 'isfirst_' + this.config.splash.whatsNewPrefix + encodeURIComponent(utils.getAppIdFromUrl());
},
edited to add code.