Hmm, maybe browser-specific? I'm seeing results for both in your notebook:

Are there any errors in the console?

Ah, great! I had not thought to try another browser.

I was using Firefox 59.0.2 on macOS. It throws no errors in the console.

When I replace the render line to this:

voronoi.render({moveTo: console.log, lineTo: console.log});

I see some weird huge values, which Firefox probably can't handle:

664.4831297076121 -31.1735912402529
672.3576712448785 -72.0304244992434
664.4831297076121 -31.1735912402529
680.819008033027 -16.631376838536138
633.5412543174806 393.00884225846926
23813793908081870 21199061956212450
121.41720113242671 -231.98418498812734
-26277289829606750 -23392068365475628
121.41720113242671 -231.98418498812734
154.39760765467472 -237.02142549637443
...

@mbostock I suspect this is some unhandled edge case in the clipping code?

Confirmed. If you zoom out in Chrome:

This is almost certainly caused by the collinear points, but I don’t know yet whether it’s a problem with the construction of the Delaunay hull or with Voronoi clipping.

The issue here is that because the points are (nearly) collinear, some of the circumcenters have huge coordinates. We’re not doing anything special to handle these huge coordinates in voronoi.render, but we probably should clip the line segments before rendering, as we do in voronoi.renderCell.

Unfortunately, it looks like voronoi.renderCell is still broken with this fix:

Made some progress, but now I’m stuck.