WebRTC generally follows the Event copy-constructor pattern for all its events, as well as its light data-holder interfaces like

• RTCIceCandidate
• RTCSessionDescription
• Even RTCError

However, the latter misses the mark as it doesn't allow initializing members to null, causing side-effects (coersion to 0). Codepen:

const e1 = new RTCError({errorDetail: "data-channel-failure"}, "foo");
const e2 = new RTCError(e1, e1.message);

[
  "name",
  "message",
  "sdpLineNumber",
  "sctpCauseCode",
  "receivedAlert",
  "sentAlert"
].forEach(name => test(t => assert_equals(e2[name], e1[name], name)));

PASS undefined
PASS undefined
FAIL undefined: sdpLineNumber - Expected null, got 0 failed
FAIL undefined: sctpCauseCode - Expected null, got 0 failed
FAIL undefined: receivedAlert - Expected null, got 0 failed
FAIL undefined: sentAlert - Expected null, got 0 failed
2/6 tests passed
PASS finished

This seems easily fixed by changing RTCErrorInit to accept null as member inputs.