feat(store): allow to wait for the store to be in sync

Author: rayrutjes

src/store.js

@@ -337,4 +337,23 @@ export class Store {
   refresh() {
     this._helper.search();
   }
+
+  waitUntilInSync() {
+    return new Promise((resolve, reject) => {
+      if (this._helper.hasPendingRequests() === false) {
+        return resolve();
+      }
+
+      // Todo: we need to de-register the one that is not being triggered.
+      this._helper.once('searchQueueEmpty', () => {
+        resolve();
+      });
+      this._helper.once('error', error => {
+        throw new Error(error.message);
+        // Todo: implement rejection once this has a solution
+        // https://github.com/algolia/algoliasearch-helper-js/issues/502
+        // reject(error);
+      });
+    });
+  }
 }