Memoize annotation resources

src/lib/AnnotationList.js

@@ -21,8 +21,11 @@ export default class AnnotationList {
 
   /** */
   get resources() {
+    this._resources = this._resources || (() => { // eslint-disable-line no-underscore-dangle
       if (!this.json || !this.json.resources) return [];
 
       return flatten([this.json.resources]).map(resource => new AnnotationResource(resource));
+    })();
+    return this._resources; // eslint-disable-line no-underscore-dangle
   }
 }

src/lib/AnnotationPage.js

@@ -24,9 +24,12 @@ export default class AnnotationPage {
 
   /** */
   get items() {
+    this._items = this._items || (() => { // eslint-disable-line no-underscore-dangle
       if (!this.json || !this.json.items) return [];
 
       return flatten([this.json.items]).map(resource => new AnnotationItem(resource));
+    })();
+    return this._items; // eslint-disable-line no-underscore-dangle
   }
 
   /**