JSFiddle - React, Tailwind, and code Playground

HTML

<body>
  <p>Click the button to display the date as a string.</p>
  <button onclick="myFunction()">Try it</button>
  <p id="demo"></p>
</body>

JavaScript

function get_num_days(dt1, dt2) {
  var ONE_DAY=1000*60*60*24;
  
  var start_dt = new Date(dt1.toDateString())   // remove any time component
  var end_dt   = new Date(dt2.toDateString())   // remove any time component
  var days = (end_dt.getTime() - start_dt.getTime()) /ONE_DAY);
  return days;
  //if (days == 0) {return "0:" + days }
  //               {return ">0:" + days }
}

function myFunction() {
    var d1 = new Date("21 Aug 2014 8:00");
    var d2 = new Date("22 Aug 2014 8:00");
    var n = get_num_days(d1,d2);
    document.getElementById("demo").innerHTML = "hi";
}