test_turn_server.js

//https://stackoverflow.com/questions/28772212/stun-turn-server-connectivity-test
function checkTURNServer(turnConfig, timeout){ 

  return new Promise(function(resolve, reject){

    setTimeout(function(){
        if(promiseResolved) return;
        resolve(false);
        promiseResolved = true;
    }, timeout || 5000);

    var promiseResolved = false
      , myPeerConnection = window.RTCPeerConnection || window.mozRTCPeerConnection || window.webkitRTCPeerConnection   //compatibility for firefox and chrome
      , pc = new myPeerConnection({iceServers:[turnConfig]})
      , noop = function(){};
    pc.createDataChannel("");    //create a bogus data channel
    pc.createOffer(function(sdp){
      if(sdp.sdp.indexOf('typ relay') > -1){ // sometimes sdp contains the ice candidates...
        promiseResolved = true;
        resolve(true);
      }
      pc.setLocalDescription(sdp, noop, noop);
    }, noop);    // create offer and set local description
    pc.onicecandidate = function(ice){  //listen for candidate events
      if(promiseResolved || !ice || !ice.candidate || !ice.candidate.candidate || !(ice.candidate.candidate.indexOf('typ relay')>-1))  return;
      promiseResolved = true;
      resolve(true);
    };
  });   
}
//Usage:
checkTURNServer({
    url: 'turn:127.0.0.1',
    username: 'test',
    credential: 'test'
}).then(function(bool){
    console.log('is TURN server active? ', bool? 'yes':'no');
}).catch(console.error.bind(console));