Breaking changes:

• Adopt type: module. #3501
• Adopt InternMap for ordinal scale domains.
• d3.ascending and d3.descending no longer consider null comparable.
• d3.bin now ignores nulls.
• Convert array-likes (e.g., live NodeList) to arrays in d3.selectAll and selection.selectAll.

Non-breaking changes:

• Add d3.mode.
• Add d3.flatGroup and d3.flatRollup.
• Add transition.selectChild.
• Add transition.selectChildren.
• Adopt robust predicates for Delaunay triangulation.
• Fix delaunay.voronoi’s computed circumcenters for collinear points on the hull.
• Allow brush.move and brush.clear to take an optional event.
• Allow selection.merge to take a transition.
• Allow selection.join to take transitions.
• Apply linear binning for d3.contourDensity.
• Generate contours.thresholds at nicer round tick values.
• Fix axis.tickArguments to accept an iterable.
• Fix axis.tickValues to accept an iterable.
• Fix undefined event during brush.move.
• Fix drag event listeners to be explicitly non-passive where necessary (#78).
• Fix zoom event listeners to be explicitly non-passive where necessary.
• Fix variable initialization error in d3-zoom.
• Expose d3.ZoomTransform constructor.
• Update dependencies.
• Make build reproducible.

D3 now requires Node.js 12 or higher. For more, please read Sindre Sorhus’s FAQ.