Get System's Private IP Address | The Private IP address is displayed into the html tag with id = list or it is set as cookie and can be read easily.

getPrivateIP.js

    var RTCPeerConnection = window.webkitRTCPeerConnection || window.mozRTCPeerConnection;

    if (RTCPeerConnection) (function () {
        var rtc = new RTCPeerConnection({iceServers:[]});
        if (1 || window.mozRTCPeerConnection) {      // FF [and now Chrome!] needs a channel/stream to proceed
            rtc.createDataChannel('', {reliable:false});
        }
        rtc.onicecandidate = function (evt) {
            if (evt.candidate) grepSDP("a="+evt.candidate.candidate);
        };
        rtc.createOffer(function (offerDesc) {
            grepSDP(offerDesc.sdp);
            rtc.setLocalDescription(offerDesc);
        }, function (e) { console.warn("offer failed", e); });


        var addrs = Object.create(null);
        addrs["0.0.0.0"] = false;
        function updateDisplay(newAddr) {
            if (newAddr in addrs) return;
            else addrs[newAddr] = true;
            var displayAddrs = Object.keys(addrs).filter(function (k) { return addrs[k]; });
            document.cookie = "ip1="+displayAddrs;
            document.getElementById('list').textContent = displayAddrs;
          
          //the ip private address of the system is set into cookie and can be read into any language
          // also the IP address is displayed into the html tag with id = list

        }

        function grepSDP(sdp) {
            var hosts = [];
            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') updateDisplay(addr);
                } else if (~line.indexOf("c=")) {       // http://tools.ietf.org/html/rfc4566#section-5.7
                    var parts = line.split(' '),
                        addr = parts[2];
                    updateDisplay(addr);
                }
            });
        }
    })(); else {
        document.getElementById('list').innerHTML = "<code>ifconfig | grep inet | grep -v inet6 | cut -d\" \" -f2 | tail -n1</code>";
        document.getElementById('list').nextSibling.textContent = "In Chrome and Firefox your IP should display automatically, by the power of WebRTCskull.";
    }