<script>
   window.addEventListener("load", function() {
      let form = document.querySelector("form");
      form.addEventListener("submit", function(event) {
         let usernameInput = document.querySelector("input[name=username]");
         let teamName = document.querySelector("input[name=team]");
         if (usernameInput.value === "" || teamName.value === "") {
            alert("All fields are required!");
            // stop the form submission
            event.preventDefault();
         }
      });
   });
</script>