Get local IP address through Javascript

getLocalIP.js

/**
 * Get Local IP Address
 * 
 * @returns Promise Object
 *
 * getLocalIP().then((ipAddr) => {
 *    console.log(ipAddr); // 192.168.0.122
 * });
 */
function getLocalIP() {
  return new Promise(function(resolve, reject) {
    // NOTE: window.RTCPeerConnection is "not a constructor" in FF22/23
    var RTCPeerConnection = /*window.RTCPeerConnection ||*/ window.webkitRTCPeerConnection || window.mozRTCPeerConnection;

    if (!RTCPeerConnection) {
      reject('Your browser does not support this API');
    }
    
    var rtc = new RTCPeerConnection({iceServers:[]});
    var addrs = {};
    addrs["0.0.0.0"] = false;
    
    function grepSDP(sdp) {
        var hosts = [];
        var finalIP = '';
        sdp.split('\r\n').forEach(function (line) { // c.f. http://tools.ietf.org/html/rfc4566#page-39
            if (~line.indexOf("a=candidate")) {     // http://tools.ietf.org/html/rfc4566#section-5.13
                var parts = line.split(' '),        // http://tools.ietf.org/html/rfc5245#section-15.1
                    addr = parts[4],
                    type = parts[7];
                if (type === 'host') {
                    finalIP = addr;
                }
            } else if (~line.indexOf("c=")) {       // http://tools.ietf.org/html/rfc4566#section-5.7
                var parts = line.split(' '),
                    addr = parts[2];
                finalIP = addr;
            }
        });
        return finalIP;
    }
    
    if (1 || window.mozRTCPeerConnection) {      // FF [and now Chrome!] needs a channel/stream to proceed
        rtc.createDataChannel('', {reliable:false});
    };
    
    rtc.onicecandidate = function (evt) {
        // convert the candidate to SDP so we can run it through our general parser
        // see https://twitter.com/lancestout/status/525796175425720320 for details
        if (evt.candidate) {
          var addr = grepSDP("a="+evt.candidate.candidate);
          resolve(addr);
        }
    };
    rtc.createOffer(function (offerDesc) {
        rtc.setLocalDescription(offerDesc);
    }, function (e) { console.warn("offer failed", e); });
  });
}