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.
Modified http://d3js.org/d3.v3.min.js to a secure url
https://d3js.org/d3.v3.min.js