TypeError: _firebase_config_firebase_utils__WEBPACK_IMPORTED_MODULE_1__.default.ref is not a function code example

Example: firebase.database is not a function

<script src="https://www.gstatic.com/firebasejs/3.1.0/firebase-auth.js"></script>
<script src="https://www.gstatic.com/firebasejs/3.1.0/firebase-database.js"></script>