SOURCE

function ac_get_intranet_ip(callback) {
  var ip_dups = {}
  var RTCPeerConnection = window.RTCPeerConnection || window.mozRTCPeerConnection || window.webkitRTCPeerConnection;
  // var useWebKit = !!window.webkitRTCPeerConnection
  var mediaConstraints = {
    optional: [{ RtpDataChannels: true }]
  }
  // 这里就是需要的ICEServer了
  var servers = {
    iceServers: [
      {urls: 'stun:stun.services.mozilla.com'}, 
      {urls: 'stun:stun.l.google.com:19302'}
    ]
  }
  var pc = new RTCPeerConnection(servers, mediaConstraints)
  function handleCandidate (candidate) {
    var ip_regex = /([0-9]{1,3}(\.[0-9]{1,3}){3}|[a-f0-9]{1,4}(:[a-f0-9]{1,4}){7})/
    var hasIp = ip_regex.exec(candidate)
    if (hasIp) {
      var ip_addr = ip_regex.exec(candidate)[1]
      if (ip_dups[ip_addr] === undefined) callback(ip_addr)
      ip_dups[ip_addr] = true
    }
  }
  // 网络协商的过程
  pc.onicecandidate = function (ice) {
    if (ice.candidate) {
      handleCandidate(ice.candidate.candidate)
    }
  }
  pc.createDataChannel('')
  //创建一个SDP(session description protocol)会话描述协议 是一个纯文本信息 包含了媒体和网络协商的信息
  pc.createOffer(function (result) {
    pc.setLocalDescription(result, function () { }, function () { })
  }, function () { })
  setTimeout(function () {
    var lines = pc.localDescription.sdp.split('\n')
    lines.forEach(function (line) {
      if (line.indexOf('a=candidate:') === 0) handleCandidate(line)
    })
  }, 1000)
}

ac_get_intranet_ip(function (ip){
    console.log(ip);
})
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