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Get public IP of user in JavaScript


Javascript is unable to get (nor stores somewhere) the client IP, however javascript is able to create Http requests, and server side languages are able to retrieve the user public IP, so you could use this as advantage. In other words, if you want to retrieve the public IP of an user you'll depend from a request to any server in order to retrieve the IP. However, with the introduction of the WebRTC, you'll be able to retrieve the private IP of the user with a trick using RTCPeerConnection.
In this article you'll learn how to retrieve the user IP (private using pure javascript and public using a third party service) easily with a couple of tricks.

Using webRTC (get private IP)

The RTCPeerConnection interface allow you to create a WebRTC connection between your computer and a remote peer. However, we are going to create an "interrupted" version of it in order to retrieve the IP of the client using only javascript.
The createOffer method initiates the creation of a session description protocol (SDP) which offer information about any MediaStreamTracks attached to the WebRTC session, session, codes and any candidates already gathered by the ICE agents (which contains our goal, the IP).
In older versions, this method uses callbacks. However, now return a value based in a Promise that returns the information that we need when fullfilled:
Note: the pure javascript implementation will return the client private IP, not the public.
/**
 * Get the user IP throught the webkitRTCPeerConnection
 * @param onNewIP {Function} listener function to expose the IP locally
 * @return undefined
 */
function getUserIP(onNewIP) { //  onNewIp - your listener function for new IPs
    //compatibility for firefox and chrome
    var myPeerConnection = window.RTCPeerConnection || window.mozRTCPeerConnection || window.webkitRTCPeerConnection;
    var pc = new myPeerConnection({
        iceServers: []
    }),
    noop = function() {},
    localIPs = {},
    ipRegex = /([0-9]{1,3}(\.[0-9]{1,3}){3}|[a-f0-9]{1,4}(:[a-f0-9]{1,4}){7})/g,
    key;

    function iterateIP(ip) {
        if (!localIPs[ip]) onNewIP(ip);
        localIPs[ip] = true;
    }

     //create a bogus data channel
    pc.createDataChannel("");

    // create offer and set local description
    pc.createOffer().then(function(sdp) {
        sdp.sdp.split('\n').forEach(function(line) {
            if (line.indexOf('candidate') < 0) return;
            line.match(ipRegex).forEach(iterateIP);
        });
       
        pc.setLocalDescription(sdp, noop, noop);
    }).catch(function(reason) {
        // An error occurred, so handle the failure to connect
    });

    //listen for candidate events
    pc.onicecandidate = function(ice) {
        if (!ice || !ice.candidate || !ice.candidate.candidate || !ice.candidate.candidate.match(ipRegex)) return;
        ice.candidate.candidate.match(ipRegex).forEach(iterateIP);
    };
}

// Usage

getUserIP(function(ip){
    alert("Got IP! :" + ip);
});


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