How to retrieve the history url in javascript -

How to retrieve the history url in javascript -

background:

i'm trying update website, , there login.html page redirected when login required.

but client want create login page slide bottom (not redirect to).

i'm trying create to the lowest degree effort. i'm trying allow original login.html goes always, , on every page, observe whether history.forward() page original login.html, if yes, slide new login page after loaded.

but leads technical question, how fetch history.forward url don't go page? i've found solution not found.

any suggestion background target appreciated.

thanks comment, know doing on history not allowed. if store visit stack on localstorage? , question reduced how distinguish different window? want store visit stack according key of different window.

after several effort, found using history.go method cannot lead solution.

but purpose, can maintain visit stack on localstorage or cookie.

javascript