text: firebase.auth().onAuthStateChanged(function(user) {
    if (user) {
      // User is signed in.
  
  document.getElementById("user_div").style.visibility = "visible";
  document.getElementById("login_div").style.visibility = "hidden";
  
    } else {
      // No user is signed in.
  
  document.getElementById("user_div").style.visibility = "hidden";
  document.getElementById("login_div").style.visibility = "visible";
    }
  });
  
  function signOut(){
  firebase.auth().signOut().then(function() {
    // Sign-out successful.
  }).catch(function(error) {
    // An error happened.
  });
  }