cache could be undefined

src/features/OnlineExam/Examing/ExamingEnd.vue

@@ -201,11 +201,12 @@ export default {
 
     // 清除考试过程中存储的音频
     caches.open("audios").then(function(cache) {
-      cache.keys().then(function(keys) {
-        keys.forEach(function(request) {
-          cache.delete(request);
+      cache &&
+        cache.keys().then(function(keys) {
+          keys.forEach(function(request) {
+            cache.delete(request);
+          });
         });
-      });
     });
   },