Untitled

<body>
    <h1>Sign-In</h1>

    <div class="container">
        <input id="txt_email" type="email" placeholder="Email">
        <input id="txt_password" type="password" placeholder="Password">

        <button id="btnLogin">Log In</button>
    </div>

    <script src="app.js"></script>
</body>

<body>
    <h1>Dashboard</h1>

    <script src="app.js"></script>
</body>

(function() {

    // Initialize Firebase
    var config = {
      //config info here
    };
    firebase.initializeApp(config);

    // Get elements
    var txt_email = document.getElementById("txt_email");
    var txt_password = document.getElementById("txt_password");
    var btnLogin = document.getElementById("btnLogin");

    // Add click listener to Log in button
    btnLogin.addEventListener("click", e => {
        //Get username and password
        var email = txt_email.value;
        var password = txt_password.value;
        const auth = firebase.auth();

        //Sign in
        const promise = auth.signInWithEmailAndPassword(email, password);
        promise.catch(e => console.log(e.message));
    });


    //Add a realtime authentication listener
    //fires every time an authentication state changes
    firebase.auth().onAuthStateChanged(firebaseUser => {
        if(firebaseUser)
        {
            console.log(firebaseUser);
            window.location = "dashboard.html";
        }
        else
        {
            console.log("not logged in");
        }
    });

}());