RTCIceCandidatePairStats.selected - Web APIs
that object's selectedcandidatepairid property indicates whether or not the specified transport is the one being used.
... example the function shown in this example identifies the currently-selected candidate pair from a statistics report by first iterating over each report, looking for a transport report; when one is found, that transport's selectedcandidatepairid is used to get the rtcicecandidatepair describing the connection.
... function getcurrentcandidatepair(statsresults) { statsresults.foreach(report => { if (report.type === "transport") { currentpair = statsresults.get(report.selectedcandidatepairid); } }); if (!currentpair) { statsresults.foreach(report => { if (report.type === "candidate-pair" && report.selected) { currentpair = report; } }); } return currentpair; } specifications not part of any specification.

RTCIceCandidatePairStats - Web APIs
that object's selectedcandidatepairid property indicates whether or not the specified transport is the one being used.