JSFiddle - React, Tailwind, and code Playground

HTML

<script src="//ajax.googleapis.com/ajax/libs/jqueryui/1.9.2/jquery-ui.min.js"></script>
<link rel="stylesheet" href="http://ajax.googleapis.com/ajax/libs/jqueryui/1.9.2/themes/vader/jquery-ui.css">
                       <br class="clear"/>
                <label id="l" style="width:80px;">From:</label>
                <input class="datepicker"  type="text" size="37" onblur="" value="" style="width:auto;" name="user_from[]"/>
                <br class="clear"/>
                <label id="l" style="width:80px;">To:</label>
                <input class="datepicker"  type="text" size="37" onblur="" value="" style="width:auto;" name="user_to[]"/>
                <br class="clear"/>

<div id="add_user1" style="display: none;" >**

<label id="l" style="width:80px;">From:</label><input class="datepicker" type="text" size="37" onblur="" value="" style="width:auto;" name="user_from[]" /><br class="clear"/>
<label id="l" style="width:80px;">To:</label><input class="datepicker"  type="text" size="37" onblur="" value="" style="width:auto;" name="user_to[]"/><br class="clear"/></div>
<input type="button" id="add_user1()" onclick="add_user('add_user1')" name="btn" value="Add More!" /><br>
                <br class="clear"/>

JavaScript

$( ".datepicker" ).datepicker();

var counter = 0;
function add_user(FieldName) {
  counter++;
  var newFields = document.getElementById(FieldName).cloneNode(true);
  newFields.id = '';
  newFields.style.display = 'block';
  var newField = newFields.childNodes;
  for (var i=0;i<newField.length;i++) {
    var theName = newField[i].name
    if (theName)
      newField[i].name = theName + counter;
  }
  var insertHere = document.getElementById(FieldName);
  insertHere.parentNode.insertBefore(newFields,insertHere);

  $(newFields).find('.datepicker').datepicker();
}