I saw a question at this link because I have a similar situation and I wanted to comment but unfortunately I do not have enough rep to do so. I would like some clarification on it.

in Tor Arne Falk's question : He displayed a script that he used to manage logged in users and logged out users like so ⬇️

<script>
    const auth = firebase.auth()
    auth.onAuthStateChanged((user) => {
      if (user) {
        document.getElementById("body").style.display = "block";
      } else {
        window.location.replace("/login.html");
      }
    });
</script>

My question is do you put that script in every html after auth ( & except auth) to check if a user is logged in or not to display content in that page after logging in or redirect them to the auth page

further more Firebase is a type="module" so a common issue with modules is that we cant import firebase outside a module meaning we cant read data from the firebase.js (handling auth & database) to a different script, example: using Tor Arne Falk script (as is) on different html pages for the same cause I believe it will not work.

please share some ideas on if it possible to read data outside the module I would like an example to help me get started if not what should I do within my firebase.js file to ensure a user is logged in across every other page to prevent them from hitting the back button and seeing that that they are still logged in or link jumping (skipping my auth page and going to a page only logged in users are supposed to see without logging in) I hope I make sense!🤔