d3.geoAlbersUsa()
This is a U.S.-centric composite projection of three d3.geoConicEqualArea projections: d3.geoAlbers is used for the lower forty-eight states, and separate conic equal-area projections are used for Alaska and Hawaii. Note that the scale for Alaska is diminished: it is projected at 0.35× its true relative area. This diagram by Philippe Rivière illustrates how this projection uses two rectangular insets for Alaska and Hawaii:
See d3-composite-projections for more examples.