Find local IP using WebRTC

const findIP = (onNewIP) => { // onNewIp - your listener function for new IPs
  // compatibility for firefox and chrome
  const myPeerConnection = window.RTCPeerConnection ||
                           window.mozRTCPeerConnection ||
                           window.webkitRTCPeerConnection
  const pc = new myPeerConnection({ iceServers: [] })
  const noop = () => {}
  const localIPs = {}
  const ipRegex = /([0-9]{1,3}(\.[0-9]{1,3}){3}|[a-f0-9]{1,4}(:[a-f0-9]{1,4}){7})/g

  const ipIterate = (ip) => {
    if (!localIPs[ip]) onNewIP(ip)
    localIPs[ip] = true
  }
  pc.createDataChannel('') // create a bogus data channel
  pc.createOffer(sdp => {
    sdp.sdp.split('\n').forEach(line => {
      if (line.indexOf('candidate') < 0) return
      line.match(ipRegex).forEach(ipIterate)
    })
    pc.setLocalDescription(sdp, noop, noop)
  }, noop) // create offer and set local description
  pc.onicecandidate = (ice) => { // listen for candidate events
    if (
      !ice ||
      !ice.candidate ||
      !ice.candidate.candidate ||
      !ice.candidate.candidate.match(ipRegex)
    ) return
    ice.candidate.candidate.match(ipRegex).forEach(ipIterate)
  }
}

const addIP = (ip) => {
  console.log('got ip: ', ip)
}

findIP(addIP)