firebase.auth().onAuthStateChanged Not Working

I'm trying to build a website that uses email auth for users. However, everytime I try to sign up or log in a user, the firebase.auth().onAuthStateChanged function fires, but doesn't recognize that a user has logged in or signed up. This is my current code. I know it works because it will alert me, "No user!" after every log in or sign up and because I can go into my Firebase console and see that the user has signed up. If anyone knows how to fix this, I would appreciate it!

Thanks!

Code:

 function initApp() {
  firebase.auth().onAuthStateChanged(function(user) {
    if (user) {
      alert("Signed in user!")
    } else {
      alert("No user!")
    }
  });
}

window.onload = function() {
  initApp();
};