The equatorial aspect of the Peirce quincuncial projection, which is available in d3-geo-projection. By setting the clip angle to 90°, you can produce the Adams hemisphere-in-a-square projection.
Changed /mbostock/raw/4090846/world-50m.json to a local referenece
https://d3js.org/d3.v4.min.js
https://d3js.org/d3-geo-projection.v1.min.js
https://d3js.org/topojson.v1.min.js