JavaScriptでグローバルIPを取得する(パブリックSTUNサーバーを利用)

function getIPAddresses() {
  const S = "stun.l.google.com:19302";

  return new Promise(resolve => {
    const pc = new RTCPeerConnection({
      iceServers: [
        {
          urls: ["stun:" + S]
        }
      ]
    });

    const rslt = [];
    pc.onicecandidate = e => {
      if (!e.candidate) {
        return resolve(rslt);
      }
      const [ip, , , type] = e.candidate.candidate.split(" ", 8).slice(4);
      if (type == "srflx") {
        rslt.push(ip);
      }
    };

    pc.onnegotiationneeded = async () => {
      await pc.setLocalDescription(await pc.createOffer());
    };

    pc.createDataChannel("");
  });
}