Including a 'class' attr causes line ghosting

[Adam Van Aken]

The path and/or line elements in the content graph are added every zoom/pan redraw, rather than updated/replaced.

Steps to reproduce:

1. Open the code sandbox from the docs: https://codesandbox.io/s/muddy-cdn-ibl5x?from-embed

2. Add a class attribute:

3. Pan/zoom graph and notice the ghosting:

[Mauricio Poppe]

I believe this is happening because setting data.*.attr.class is overriding the class set by functionPlot on each datum so when there's the d3 data binding it appears to functionPlot that this is a new datum.

A small workaround would be to merge the class with functionPlot's class, on the downside it'd not be possible to remove a class on update, I think that could work.

[Mauricio Poppe]

It should be fixed in https://github.com/mauriciopoppe/function-plot/releases/tag/v1.23.3, thanks for the bug report 🙏🏼.