index.html

<!DOCTYPE html>
<html>
  <body>
    <script>
        function checkUser() {
            var username = document.getElementById("username").value;
            var password = document.getElementById("password").value;
            var correctUser = "username";
            var correctPassword = "password";
            if (username == correctUser && password == correctPassword) {
                document.getElementById("correct").textContent = "True";
            }
        }
    </script>
    <label for="username">Username:</label>
    <input type="text" id="username" name="username"><br><br>
    <label for="password">Password:</label>
    <input type="password" id="password" name="password"><br><br>
    <button type="button" id="submit" onClick="checkUser()">Submit</button>
    <label id="correct">False</label>
  </body>
</html>