storage.js: Add method `on` to `StorageAwareSet`

public/js/icinga/behavior/collapsible.js

@@ -22,12 +22,12 @@
         this.defaultVisibleRows = 2;
         this.defaultVisibleHeight = 36;
 
-        $(window).on('StorageAwareSetAdd', { self: this }, this.onExternalExpansion);
-        $(window).on('StorageAwareSetDelete', { self: this }, this.onExternalCollapse);
         this.state = new Icinga.Storage.StorageAwareSet.withStorage(
             new Icinga.BehaviorStorage('collapsible'),
             'expanded'
-        );
+        )
+            .on('add', { self: this }, this.onExternalExpansion)
+            .on('delete', { self: this }, this.onExternalCollapse);
     };
     Collapsible.prototype = new Icinga.EventListener();
 

public/js/icinga/storage.js

@@ -250,6 +250,27 @@
             }, this);
         },
 
+        /**
+         * Register an event handler to handle storage updates
+         *
+         * Available events are: add, delete
+         *
+         * @param   {string}    event
+         * @param   {object}    data
+         * @param   {function}  handler
+         *
+         * @returns {this}
+         */
+        on: function(event, data, handler) {
+            $(window).on(
+                'StorageAwareSet' + event.charAt(0).toUpperCase() + event.slice(1),
+                data,
+                handler
+            );
+
+            return this;
+        },
+
         /**
          * Return the number of (unique) elements in the set
          *