JSFiddle - React, Tailwind, and code Playground

by L W

HTML

<form action="">
  <label class="fa fa-calendar">
        <input id="startDate" name="start_at" placeholder=" " class="data-charts" type="text" value="05/03/2017">
  </label>
  <label class="fa fa-calendar">
        <input id="endDate" name="end_at" placeholder=" " class="data-charts" type="text" value="04/04/2017">
  </label>
</form>

JavaScript

var data_inicial = document.getElementById("startDate").value;
var data_final = document.getElementById("endDate").value;

var date1 = new Date(data_inicial);
var date2 = new Date(data_final);
var timeDiff = Math.abs(date2.getTime() - date1.getTime());
var diffDays = Math.ceil(timeDiff / (1000 * 3600 * 24)); 
if(diffDays <= 30)
{
alert("diferença menor que 30 dias")
}