JSFiddle - React, Tailwind, and code Playground

HTML

<div id="timer"></div>

JavaScript

setInterval(function()
{
  var end = new Date(2018, 06, 1, 0, 0, 0, 0);
  var now = new Date();

  var timer = '';
  var diff = end - now;

  var milliseconds = Math.floor(diff / 1000);
  var milliseconds_ = diff % 1000;

  var seconds = Math.floor(milliseconds / 60);
  var seconds_ = milliseconds % 60;

  var minutes = Math.floor(seconds / 60);
  var minutes_ = seconds % 60;

  var hours = Math.floor(minutes / 24);
  var hours_ = minutes % 24;

  var days = Math.floor(hours / 24);
  var days_ = hours % 24;

  timer = days_+'д '+hours_+':'+minutes_+':'+seconds_;

  document.getElementById('timer').innerHTML = timer;
},1000);