add parentEl.whenReady in mapFeature.whenReady as a pre-condition, avoid racing

Author: yhy0217

src/map-feature.js

@@ -658,27 +658,29 @@ export class MapFeature extends HTMLElement {
     map.setView(center, this.getMaxZoom(), { animate: false });
   }
   whenReady() {
-    return new Promise((resolve, reject) => {
-      let interval, failureTimer;
-      if (this._featureGroup) {
-        resolve();
-      } else {
-        let featureElement = this;
-        interval = setInterval(testForFeature, 200, featureElement);
-        failureTimer = setTimeout(featureNotDefined, 5000);
-      }
-      function testForFeature(featureElement) {
-        if (featureElement._featureGroup) {
+    return this._parentEl.whenReady().then(() => {
+      return new Promise((resolve, reject) => {
+        let interval, failureTimer;
+        if (this._featureGroup) {
+          resolve();
+        } else {
+          let featureElement = this;
+          interval = setInterval(testForFeature, 200, featureElement);
+          failureTimer = setTimeout(featureNotDefined, 5000);
+        }
+        function testForFeature(featureElement) {
+          if (featureElement._featureGroup) {
+            clearInterval(interval);
+            clearTimeout(failureTimer);
+            resolve();
+          }
+        }
+        function featureNotDefined() {
           clearInterval(interval);
           clearTimeout(failureTimer);
-          resolve();
+          reject('Timeout reached waiting for feature to be ready');
         }
-      }
-      function featureNotDefined() {
-        clearInterval(interval);
-        clearTimeout(failureTimer);
-        reject('Timeout reached waiting for feature to be ready');
-      }
+      });
     });
   }
 }