A dead simple example of the just released d3-shape module of the upcoming fourth version of d3.js. The example shows two SVG paths created using Catmull-Rom interpolation. d3-path is also loaded as a dependency for generating SVG paths.
Noticed that I skipped the module configuration and building phase of d3 v4 because i) I am not yet accustomed to it, and ii) I just wanted to quickly play with the new API.
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<html lang="en">
<head>
<meta charset="utf-8">
<title>d3-shape</title>
<link rel="stylesheet" href="index.css">
<script src="https://d3js.org/d3.v3.min.js"></script>
<script src="d3-path.js"></script>
<script src="d3-shape.js"></script>
</head>
<body>
<svg></svg>
<script src="index.js"></script>
</body>
</html>
Modified http://d3js.org/d3.v3.min.js to a secure url
https://d3js.org/d3.v3.min.js