This event is called on window every time the active history state changes, with the current state as the callback parameter:

window.onpopstate = event => {
  console.log(event.state)
}

or

window.addEventListener('popstate', event => {
  console.log(event.state)
})

will log the new state object (the first parameter passed to pushState or replaceState) every time you call history.back(), history.forward() or history.go().

Lessons in this unit: