What changes when you use the Pages control? A filter? That API lists the events it listens for, and what you want is not on the list. You'll have to listen for something else, or change what's happening on the viz/dashboard to initiate an event that the API DOES listen for.
Dear MICHAEL GILLESPIE, Thank you for your comment. I confirmed that current API doesn't detect page change event. > https://github.com/tableau/extensions-api/issues/265 So I will change my implementation. Regards, hiro