JSFiddle - React, Tailwind, and code Playground

HTML

<form id="form">
	<label>Deadline:</label>	<input type="date" id="deadline"><br>
  <input id="create" type="button" value="Create" />
</form>

<div id="result"></div>

JavaScript

$(function(){
	function diff(deadline) {
    var today = new Date(new Date().toDateString());
    var diffTime = Math.abs(deadline.getTime() - today.getTime());
    var diffDays = Math.ceil(diffTime / (1000 * 60 * 60 * 24));
    return diffDays;
  }
  
  function showDiff(date) {
    $('#result').html(date);
  }
  
  $('#create').click(function () {
    var deadline = new Date($('#deadline').val());
    deadline.setMinutes(deadline.getMinutes() + deadline.getTimezoneOffset());
    showDiff(diff(deadline));
    localStorage.setItem('deadline', deadline);
  });
  var savedDeadline = localStorage.getItem('deadline')
  if (savedDeadline) {
  	var date = new Date(savedDeadline);
    showDiff(diff(date));
  }
});