To install GeoScript JS, download the latest release and extract the zip archive.
After extracting the release archive, you can open the GeoScript shell console and import any of the GeoScript modules by running bin/geoscript.
~/geoscript-js$ ./bin/geoscript
>> var geom = require("geoscript/geom");
>> var p1 = new geom.Point([0, 0]);
>> var p2 = new geom.Point([10, 20]);
>> p1.distance(p2);
22.360679774997898
>> var poly = p2.buffer(23);
>> poly.contains(p1);
true
>> quit()