Prevent duplicate tabs chrome javascript

1. How do I Spam duplicate tabs?
2. How do you prevent a user from opening the same URL in multiple tabs in the same browser?

How do I Spam duplicate tabs?

Press Alt+Shift+D to duplicate the current tab (Option+Shift+D on Mac).

How do you prevent a user from opening the same URL in multiple tabs in the same browser?

You cannot (and should not) do that. User can always just open use another browser or another computer to open another view onto the web site. So, basically you cannot ever prevent this. Your web-site should be able to handle multiple tabs viewing the same state.