JSFiddle - React, Tailwind, and code Playground

HTML

<span id="timer"></span>

JavaScript

var date = new Date(2015, 6, 31); // !!! Maanden beginnen bij 0, dus Januari is 0.
var now = new Date();
var diff = (date.getTime()/1000) - (now.getTime()/1000);
var count=diff;
var counter=setInterval(timer, 1000); //1000 will  run it every 1 second

function timer()
{
  count=count-1;
  if (count <= 0)
  {
     clearInterval(counter);
     return;
  }

 document.getElementById("timer").innerHTML=count + " secs"; // watch for spelling
}