This is related to #269 and #267 from what I can see, but I will post here as a note that might help other people.

The new export mechanism generated by Rollup JS seems to have exported topojson as a named module. This means you can no longer load the module via it's file path when you use it in AMD / RequireJS you have to create an alias, e.g.

v1.6.20

//This worked okay
define(['bower_components/topojson/topjson'], function(topojson) {
  console.log(topojson.feature);
})

v1.6.21

require.config({
  paths: {
    topojson: 'bower_components/topojson/topjson'
  }
});

define(['topojson'], function(topojson) {
  console.log(topojson.feature);
})

http://requirejs.org/docs/api.html#modulename
http://stackoverflow.com/questions/19720646/named-module-vs-unnamed-module-in-requirejs