Presumably the error event (from DNS I think) should be passed on to the callback. It makes this library un-usable as it causes the whole app to crash out. This is with using a non-existant hostname:

$ node lib/entities/Ntp.js
{ [Error: getaddrinfo EIO] code: 'EIO', errno: 'EIO', syscall: 'getaddrinfo' }

events.js:72
        throw er; // Unhandled 'error' event
              ^
Error: getaddrinfo EIO
    at errnoException (dns.js:37:11)
    at Object.onanswer [as oncomplete] (dns.js:124:16)

If connection gets closed due to external event
error is experienced after attempt to send 'ntpData'.

Connection should be only closed if open :)

Details:

dgram.js:420
    throw new Error('Not running'); // error message from dgram_legacy.js
          ^
Error: Not running
    at Socket._healthCheck (dgram.js:420:11)
    at Socket.close (dgram.js:327:8)
    at /opt/cos-medico/new/node_modules/ntp-client/lib/ntp-client.js:80:24
    at dgram.js:297:21
    at asyncCallback (dns.js:68:16)
    at Object.onanswer [as oncomplete] (dns.js:124:7)

we know actually it aint a front end tech~ yes, we mean nodejs.

I think that's how normal ntp works
Just ignore a value if it is not in the range [Q1-k(Q3-Q1),Q3+k(Q3-Q1)], where Q1 and Q3 are the 25th and 75th percentiles, k is a constant and to calculate a percentile you just do:

data_set = data_set.sort();
for (var i=0;i<data_set.length;i++){
    if (i>=data_set.length*percentile/100){
           answer = data_set[i];
           break;
    }
}

Yes, I just read all that on wikipedia

I'd like to sync many browsers

If the dgram client errors, the callback receives an Error object, but if there is a timeout a String gets passed as the error callback which makes appropriate error handling a real pain:

https://github.com/moonpyk/node-ntp-client/blob/master/lib/ntp-client.js#L52