count exact 5 minutes from date

Question

I faced up with problem to calculate exact 5 minutes from time. Here the scenario, from the server response I get dateTime in format YYYY-MM-DD HH:mm:ss after that I show up local timer on page which counts 5 minutes after that time. I do it with momentjs.

var output = document.getElementById('out');

var fromCount = '2017-02-22 00:23:50';
var toMins = moment(fromCount).add(5, 'minutes');
var toMinsCount = setInterval(function(){
  var now = moment();
  var diff = moment(toMins - now).format('mm:ss');
  if(diff==='00:00'){
    clearInterval(toMinsCount);
    // something more here
    output.innerText = 'times up change fromCount data time';
  }
  if(now>toMins){
    clearInterval(toMinsCount);
    output.innerText = 'change fromCount data time';
  } else {
    output.innerText = diff;
  }
},1000);

<script src="https://cdnjs.cloudflare.com/ajax/libs/moment.js/2.17.1/moment.min.js"></script>

<div id="out"></div>

Everything works nice BUT, sometimes when I add 5 minutes to date counter starts count from 5:13 or bit higher, it occurs when for example data from count = '2017-02-22 00:30:50' and now date = '2017-02-22 00:30:15'. So how can I avoid this problem and show local counter exact 5:00 minutes?

I need to count it from servers time because my counter depends on special event. And I should show for each user came to page same time from the moment server has catch. In local way each user will see it's own 5 min timer.

Answer 1

Ok, here the solution that fits my needs.

function count5min(value) {
    $http.get('https://testfate.ru/time').then(function (resp) {
      // getting dateTime fromServer

      var realTime, toMins, diff;

      realTime = moment(resp.data.time).valueOf();
      diff = moment().valueOf() - realTime;

      var beforeStart = moment(value);

      toMins = moment(beforeStart).add(5, 'minutes');

      var toMinsCount = setInterval(function () {
        var now = moment().subtract(diff, 'milliseconds');
        var difference = moment(toMins - now).format('mm:ss');
        if (difference === '00:00') {
          clearInterval(toMinsCount);
        }
        if (now > toMins) {
          clearInterval(toMinsCount);
        } else {
          $(el).find('.short-timer').text(difference);
        }
      }, 1000);

    }, function (err) {
      console.error(err);
    });
  }

So what I do is, getting time from server, found difference between local time and server time in ms, then in interval function subtract this difference from local time. Works like a charm for me. My friend suggest this idea to me.