fix getKey not working on IE11

src/matrix/storage/idb/QueryTarget.js

@@ -42,7 +42,15 @@ export class QueryTarget {
     }
 
     getKey(key) {
-        return reqAsPromise(this._target.getKey(key));
+        if (this._target.supports("getKey")) {
+            return reqAsPromise(this._target.getKey(key));
+        } else {
+            return reqAsPromise(this._target.get(key)).then(value => {
+                if (value) {
+                    return value[this._target.keyPath];
+                }
+            });
+        }
     }
 
     reduce(range, reducer, initialValue) {

src/matrix/storage/idb/Store.js

@@ -23,6 +23,14 @@ class QueryTargetWrapper {
         this._qt = qt;
     }
 
+    get keyPath() {
+        if (this._qt.objectStore) {
+            return this._qt.objectStore.keyPath;
+        } else {
+            return this._qt.keyPath;
+        }
+    }
+
     supports(methodName) {
         return !!this._qt[methodName];
     }

src/matrix/storage/idb/stores/PendingEventStore.js

@@ -52,13 +52,7 @@ export class PendingEventStore {
 
     async exists(roomId, queueIndex) {
         const keyRange = IDBKeyRange.only(encodeKey(roomId, queueIndex));
-        let key;
-        if (this._eventStore.supports("getKey")) {
-            key = await this._eventStore.getKey(keyRange);
-        } else {
-            const value = await this._eventStore.get(keyRange);
-            key = value && value.key;
-        }
+        const key = await this._eventStore.getKey(keyRange);
         return !!key;
     }