Subscribe method causes error in IE11

Import and creating client is okay for IE11 but when using the subscribe method, it causes this error:

The application will stop into a white blank screen. It doesn't happen when in Chrome. See my implementation:

Edit #1: I was able to confirm that it's caused by the subscribe method, because I was trying to comment and uncomment SocketCluster related codes. When I uncomment the line for unsubscribe, the error occurs in IE11.

Edit #2: Tried to downgrade the version to 13, it seems the error doesn't happen. But I can't use it with a server in version 16.

Details:
SocketCluster Client Version: 16.0.1
Vue 2: 2.6.11

Expected: To work in IE11 similarly as in Chrome.
Actual: White blank screen in IE11 with syntax error. Working smoothly in Chrome.

Start by reproducing the issue in IE11 with SocketCluster Client 16.0.1, using the subscribe and unsubscribe calls shown in the report, and compare with Chrome and version 13. The report names no source file or test; done means the IE11 syntax error and resulting blank screen no longer occur while the client remains compatible with a version 16 server.