Back pressed event

Question

exists "onBackPressed" or similar for javascript?

Answer 1

If by 'back pressed event' you mean event listener for the previous page button of the browser, there isn't... but you have an event listener attachable to the 'window' object 'onbeforeunload':
https://developer.mozilla.org/en-US/docs/Web/API/WindowEventHandlers/onbeforeunload