As always, we'll need an index.html file to house our SVG code. Let's create the file and add the following code to it:
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title></title>
<script src="https://d3js.org/d3.v5.min.js"></script>
</head>
<body>
<svg>
<g></g>
</svg>
<script src="app.js" charset="utf-8"></script>
</body>
</html>