Merge pull request #2879 from murgatroid99/grpc-js-xds_preserve_stream_type_state

grpc-js-xds: Preserve resource type version and nonce when unsubscribing

Author: murgatroid99

packages/grpc-js-xds/src/xds-client.ts

@@ -458,9 +458,6 @@ class AdsCallState {
     if (authorityMap.size === 0) {
       typeState.subscribedResources.delete(name.authority);
     }
-    if (typeState.subscribedResources.size === 0) {
-      this.typeStates.delete(type);
-    }
     this.updateNames(type);
   }