issue #8916 pr fix #8930

This example opens two window with same front-end code, but the function is related to the current window label, so they are completely independent.

The front-end uses useEffect to listen a event with the name of the windowLabel after the page loads, and unlisten to clear the side-effect. The back-end creates a command fn called emit, which sends a message to the front-end with the eventName windowLabel, and clicking the button on the front-end invokes the emit command.