This is the VCL & JS implementation of the User-Agent normalisation used within the polyfill-service and the polyfill-library.
For a request which was the user-agent Chrome 71.1:
import "normalise-user-agent.vcl";
sub vcl_recv {
call normalise_user_agent_1_0_6;
# req.http.normalized_user_agent_family = "chrome";
# req.http.normalized_user_agent_major_version = "71";
# req.http.normalized_user_agent_minor_version = "1";
# req.http.normalized_user_agent_patch_version = "0";
# req.http.Normalized-User-Agent = "chrome/71.1.0";
}
const UA = require('@financial-times/polyfill-useragent-normaliser');
const useragent = new UA(request.headers['user-agent']);
console.log(useragent.isUnknown()); // false
console.log(useragent.satisfies("<50")); // false
console.log(useragent.satisfies(">50")); // true