Uncaught TypeError: firebase.database is not a function at writeData ((index):90) at HTMLButtonElement.onclick ((index):97) 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>