The upper range value should be rounded down.

[Mike Bostock]

Currently I say:

range0 = range[0] + 0.5,
range1 = range[range.length - 1] + 0.5,

But wouldn’t this be better?

range0 = range[0] + 0.5,
range1 = range[range.length - 1] - 0.5,

[Mike Bostock]

This is a bad idea because it makes the upper corner of the path domain inconsistent with the last tick, which is often coincident with the end of the path domain. Better is to offset the scale range by one pixel:

x.range([0, width - 1]);