How to hide back button?

What if the proper way to hide a back button?
I have a back button which calls

router.back()

router.back()

but I want to hide this button if

router.back()

router.back()

would go out of the app. (For example, if you open a new tab and then go to the URL of the app,

router.back()

router.back()

will work until it will go back to the new tab).