How to get local/internal IP with JavaScript

Question

How can I get the local client IP using WebRTC.

I don't need the REMOTE_ADDR of the client but his local network IP. I've seen this before on websites like sharedrop.com, it recognizes computer within the same network using WebRTC.

In PHP I do this to get the clients remote IP:

<?php
  echo $_SERVER["REMOTE_ADDR"]; // which would return 72.72.72.175
?>

I looked through stackoverflow but every question is answered using the remote addr.

How can I get my local IP (192.168.1.24 for example) with JavaScript instead of the remote addr.

Answer 1

UPDATE

Unfortunately the below answer no longer works as browsers have changed this behavior due to security concerns. See this StackOverflow Q&A for more details.

---

where I took code from --> Source

You can find a demo at --> Demo

I have modified the source code, reduced the lines, not making any stun requests since you only want Local IP not the Public IP, the below code works in latest Firefox and Chrome:

    window.RTCPeerConnection = window.RTCPeerConnection || window.mozRTCPeerConnection || window.webkitRTCPeerConnection;   //compatibility for firefox and chrome
    var pc = new RTCPeerConnection({iceServers:[]}), noop = function(){};      
    pc.createDataChannel("");    //create a bogus data channel
    pc.createOffer(pc.setLocalDescription.bind(pc), noop);    // create offer and set local description
    pc.onicecandidate = function(ice){  //listen for candidate events
        if(!ice || !ice.candidate || !ice.candidate.candidate)  return;
        var myIP = /([0-9]{1,3}(\.[0-9]{1,3}){3}|[a-f0-9]{1,4}(:[a-f0-9]{1,4}){7})/.exec(ice.candidate.candidate)[1];
        console.log('my IP: ', myIP);   
        pc.onicecandidate = noop;
    };
    

what is happening here is, we are creating a dummy peer connection, and for the remote peer to contact us, we generally exchange ice candidates with each other. And reading the ice candiates we can tell the ip of the user.