This writeup is good for describing what should be possible, but it isn't good for helping to reproduce your result.

I pasted in all your example code and it draws a blank svg. I can see the DOM nodes exist but they have no colour.

For example, you don't talk about what the variable `rectWidth` is, but it is shown in your code.

For example, you said, "The next steps I did are to construct lines for the links, and beautify the nodes, by adding text, images and borders for each of the nodes." But you don't show code for how you did it.

I think you should improve this article by including an example GitHub repo or update the code examples to be more fully qualified.

As a reader, I should be able to achieve something after following your example.